Streets were blocked off as police fired tear gas and beat protesters with batons, amid reports that an unconfirmed number of monks had been shot dead.
The day began with riot police clashing with monks attempting to force their way past barricades blocking off the Shwedagon Pagoda, Myanmar's holiest shrine, and a rallying point for demonstrators.
The ruling military junta had earlier forbidden all public gatherings of more than five people and imposed a night-time curfew. The moves came after eight days of anti-government marches led by monks in Rangoon and other areas of the country, including a 100,000-strong demonstration on Monday in the capital.
Three of the country's most famous anti-junta public figures, the poet Aung Way, actor Kyaw Thu and the comedian Zarganar have been detained, and there are unconfirmed reports from dissident groups of more arrests.
The protests, which are the biggest for more than two decades, began last month when the junta drastically raised the price of fuel, leaving many people unable to afford even a journey to work.
The ruling-junta seized power in 1988, and although a general election was subsequently held in 1990, the military authorities refused to honor the results when pro-democracy leader Aung San Suu Kyi's National League for Democracy Party won.
Aung San Suu Kyi, the daughter of the country's independence hero General Aung San, has been under house arrest for 11 of the past 18 years. Her latest period of detention began in May 2003. She made an appearance at the gates of her house on Saturday, reportedly praying with monks.
The White House was said to be "very troubled" by news of the shootings. British Prime Minister Gordon Brown earlier called for a UN Security Council meeting on Myanmar, saying there would be "no impunity" for anyone guilty of violating human rights in the country.
The last anti-junta demonstrations in Myanmar were led by students in 1988. Security forces opened fire on crowds, and around 3,000 people were killed.
The Myanmarese ruling junta is the State Peace and Development Council (SPDC), known as the State Law and Order Restoration Council (SLORC) until 1997.
