Burmese soldiers and police are baton charging small groups of protesters who are trying to gather in Rangoon.
Security forces have sealed off the five main monasteries that were focal points of previous mass marches and are trying to prevent further protests.
Official media said nine people were killed on Thursday as troops fired tear gas and bullets to clear large crowds protesters off the streets of Rangoon.
But Australia's ambassador in Burma said the toll was probably higher.
The security presence in Rangoon is the heaviest yet, says the BBC's Jonathan Head in neighbouring Thailand.
Troops have sealed off the key monasteries and pagodas in Rangoon, including Shwedagon and Sule pagodas - the focal point for some of the larger protests earlier in the week.
All the main roads into central Rangoon have been blocked and soldiers have been progressively moving the barricades to seal off central neighbourhoods.
The security clampdown appears to have prevented monks from leaving their monasteries.
But some small groups of people have managed to assemble only to be dispersed by soldiers wielding batons.
There are reports that shots have been fired, but it is not clear if they are being fired into the crowds or overhead in warning.
One report, from AFP news agency, said shots were fired in warning after a crowd of people north of the Sule pagoda had ignored a five-minute warning to disperse.
Loudspeaker trucks have been criss-crossing the city, warning people not to protect anyone fleeing arrest.
The trucks have also announced an overnight curfew for the South Okkalapa district, the scene of Thursday's violent encounters between soldiers and protesters.
Communications cut
Burmese sources say internet access has been cut in Rangoon and is only partially available elsewhere.
Dissidents had been making use of the internet to get pictures and video of the protests and the bloody crackdown to international news outlets - who have then fed them back to Burma on the internet and satellite TV.
BBC sources in Burma have said that international mobile phone signals have been interrupted and soldiers are searching people for cameras and mobile phones.
One of the people killed on Thursday was a Japanese video journalist. According to the official accounts, eight protesters were also killed. One man was reported killed on Wednesday.
Japan said it would make an official protest over the death in Rangoon of Kenji Nagai, a video journalist for Tokyo-based news agency APF News.
Australian Ambassador Bob Davis told his country's ABC radio that the death toll might be "several multiples of the 10 acknowledged by the authorities".
He said witnesses had told embassy officials they had seen "significantly more than that number of dead being removed from the scene of the demonstrations" in Rangoon on Thursday.
Monks seized
On Thursday, soldiers and police fired into crowds of demonstrators in Rangoon and gave them 10 minutes to clear the streets or face the consequences, the Reuters news agency reported.
Eleven demonstrators and 31 soldiers were hurt, according to the official account.
Authorities were trying to stamp out the largest uprising in two decades, as it continued for its 10th day.
The popular defiance has been led by Buddhist monks but there were fewer on the streets on Thursday following overnight raids on monasteries.
There have been reports of monks being severely beaten with several hundred believed to have been arrested.
Pictures from Burma showed ransacked monasteries with pools of blood on the ground.
US President George W Bush has condemned the crackdown and has tightened sanctions on Burma's military leaders.
In talks with Chinese Foreign Minister Yang Jiechi at the White House, Mr Bush called on China, one of Burma's closest neighbours and a main trading partner, to put more pressure on the country.
He said: "Every civilised nation has a responsibility to stand up for people suffering under a brutal military regime like the one that has ruled Burma for too long."
Beijing has urged all parties to "maintain restraint", but has refused to condemn the junta.
Burma's other neighbours from Asean (the Association of South East Asian Nations), have expressed their "revulsion" over the violence at a meeting of the group's foreign ministers in New York.
BBC United Nations correspondent Laura Trevelyan says Asean members do not usually interfere in each other's internal affairs but the group is too embarrassed to ignore the world focus on what is happening on its doorstep.
In a sign that the international pressure may be having some effect, the Burmese authorities have agreed to let UN special envoy Ibrahim Gambari visit the country.
He has stopped in Singapore on his way to Burma.
Article first appeared on the BBC Website|