Security forces with tanks have overrun a square in the centre of Bahrain's capital Manama where anti-government protesters have been camped for weeks.
At least three civilians were reportedly killed after police fired on mainly Shia protesters. Officials said three police also died.
The government has imposed a curfew from 1600 (1300 GMT) to 0400 and banned all demonstrations.
The country's Sunni rulers on Tuesday called in Saudi troops to keep order.
At least two people died in clashes on Tuesday and more than 200 were injured.
The country's health minister, himself a Shia, has resigned in protest against the government's use of force, and the BBC's Caroline Hawley in Manama says Shia judges have resigned en masse.
In other developments:
Armoured vehicles moved in shortly after dawn, our correspondent says, and the security forces appear to have gained full control of the square after an operation lasting a couple of hours.
Further protests were called for 1530 local time, but shortly afterwards a military officer announced the curfew live on TV, to start just a half hour later.
Streets around Budaya Street in northern Manama were deserted on Wednesday afternoon, residents told Reuters, indicating that the call to demonstrate in the area had not been answered.
Hospital surrounded The crackdown comes a day after King Hamad Bin Isa Al Khalifa declared a three-month state of emergency.
Protesters had set up barricades in the square but they were no match for the military, our correspondent says.
An eyewitness, Dalal, told the BBC that police were firing rubber bullets. They shot at tents in the square, she said, and set fire to cooking oil inside.
"There was so much smoke we could hardly see our hands," she said. "People began retreating. When the police saw that we were moving they ran towards us."
Tyres were burnt to alert people in surrounding villages to the crackdown but they were unable to make it through to the square to join the protests.
The security forces have now moved into Manama's financial district, reopening roads which had been blocked by protesters.
Sources at the Salmaniya hospital said it had been surrounded by troops, and no-one was being allowed in or out. The wounded are now reportedly being treated in mosques or at home.
A doctor there told the BBC troops that she and her colleagues were hiding from troops who had taken over the building, were shooting at people inside the hospital and threatening the doctors with live ammunition.
"They are all around Salmaniya medical complex with their guns and they are shooting anybody," she said.
Meanwhile a surgeon told the BBC's Bill Law that he had been called to a private hospital to operate on a man with gunshot wounds but was forced to turn back.
He said government claims that protesters were not being denied treatment were false.
"I am terrified," he added. "This is a genocide directed against the Shia."
Calls for reform Human rights groups said live rounds had been used in some parts of the city.
The protests in Bahrain - which has a population of 800,000 - began last month. The Shia majority complain of economic hardship, lack of political freedom and discrimination in jobs in favour of Sunnis.
Seven people had been killed during a month of protests prior to Tuesday's clashes.
The king reshuffled his cabinet on 26 February, replacing four ministers, including two royal family members. However, he did not sack Prime Minister Sheikh Khalifah ibn Salman al-Khalifah, who has held the office for more than 40 years.
The protesters were inspired by the recent uprisings in Tunisia and Egypt, whose long-serving presidents were forced from power after weeks of demonstrations.
The UN, US and other countries have called for restraint and a political resolution to the crisis.
But our correspondent says the prospect of dialogue recedes with every shot fired.
http://www.bbc.co.uk/news/world-middle-east-12755852
At least three civilians were reportedly killed after police fired on mainly Shia protesters. Officials said three police also died.
The government has imposed a curfew from 1600 (1300 GMT) to 0400 and banned all demonstrations.
The country's Sunni rulers on Tuesday called in Saudi troops to keep order.
At least two people died in clashes on Tuesday and more than 200 were injured.
The country's health minister, himself a Shia, has resigned in protest against the government's use of force, and the BBC's Caroline Hawley in Manama says Shia judges have resigned en masse.
In other developments:
- Largest Shia opposition group Wefaq has urged followers to avoid confrontation with authorities, and said it had not organised any protests, Reuters news agency reports
- Security forces urged people to refrain from gathering in the capital "for their own safety"
- Senior Bahrain opposition MP Abdel Jalil Khalil, quoted by Reuters, described the crackdown as a "war of annihilation"
- President Mahmoud Ahmadinejad of Iran, the major Shia power in the region, said the crackdown was unjustifiable and irreparable, and blamed the US
- The country's stock market said it had closed until further notice. Two of Bahrain's main banks - Standard Chartered and HSBC Holdings - said they had closed all their branches
Continue reading the main story
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End Quote Doctor at Salmaniya hospitalThey are all around Salmaniya medical complex with their guns and they are shooting anybody”
It is not clear whether soldiers from other Gulf states are taking part in the crackdown, but there are indications that the Saudi troops are being kept in reserve.
Our correspondent says black plumes of smoke are rising over Pearl Square, the centre of the protests, while helicopters are flying overhead. There are riot police stationed in approach roads.Armoured vehicles moved in shortly after dawn, our correspondent says, and the security forces appear to have gained full control of the square after an operation lasting a couple of hours.
Further protests were called for 1530 local time, but shortly afterwards a military officer announced the curfew live on TV, to start just a half hour later.
Streets around Budaya Street in northern Manama were deserted on Wednesday afternoon, residents told Reuters, indicating that the call to demonstrate in the area had not been answered.
Hospital surrounded The crackdown comes a day after King Hamad Bin Isa Al Khalifa declared a three-month state of emergency.
Protesters had set up barricades in the square but they were no match for the military, our correspondent says.
An eyewitness, Dalal, told the BBC that police were firing rubber bullets. They shot at tents in the square, she said, and set fire to cooking oil inside.
Manama doctor claims security forces are preventing the injured from receiving treatment
Tyres were burnt to alert people in surrounding villages to the crackdown but they were unable to make it through to the square to join the protests.
The security forces have now moved into Manama's financial district, reopening roads which had been blocked by protesters.
Sources at the Salmaniya hospital said it had been surrounded by troops, and no-one was being allowed in or out. The wounded are now reportedly being treated in mosques or at home.
A doctor there told the BBC troops that she and her colleagues were hiding from troops who had taken over the building, were shooting at people inside the hospital and threatening the doctors with live ammunition.
"They are all around Salmaniya medical complex with their guns and they are shooting anybody," she said.
Meanwhile a surgeon told the BBC's Bill Law that he had been called to a private hospital to operate on a man with gunshot wounds but was forced to turn back.
He said government claims that protesters were not being denied treatment were false.
"I am terrified," he added. "This is a genocide directed against the Shia."
Calls for reform Human rights groups said live rounds had been used in some parts of the city.
Continue reading the main story 
Mid-East unrest: Bahrain
- King Hamad, 61, has been in power since 1999
- Population 800,000; land area 717 sq km, or 100 times smaller than Irish Republic
- A population with a median age of 30.4 years, and a literacy rate of 91%
- Youth unemployment at 19.6%
- Gross national income per head: $25,420 (World Bank 2009)
There are also reports of dozens injured but our correspondent says it is difficult to get any sense of casualty numbers.
Bahrain - home to the US Navy's Fifth Fleet - is the first Gulf country to be thrown into turmoil by the wave of unrest sweeping the Arab world.The protests in Bahrain - which has a population of 800,000 - began last month. The Shia majority complain of economic hardship, lack of political freedom and discrimination in jobs in favour of Sunnis.
Seven people had been killed during a month of protests prior to Tuesday's clashes.
The king reshuffled his cabinet on 26 February, replacing four ministers, including two royal family members. However, he did not sack Prime Minister Sheikh Khalifah ibn Salman al-Khalifah, who has held the office for more than 40 years.
The protesters were inspired by the recent uprisings in Tunisia and Egypt, whose long-serving presidents were forced from power after weeks of demonstrations.
The UN, US and other countries have called for restraint and a political resolution to the crisis.
But our correspondent says the prospect of dialogue recedes with every shot fired.
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