Security forces killed at least 22 pro-democracy protesters in the Hlaingthaya suburb of Yangon on Sunday, an advocacy group said, Reuters reported.
A further 16 protesters were killed in other places, the Assistance Association for Political Prisoners (AAPP) said, as well as one policeman, making it the bloodiest day since the Feb 1 coup against elected leader Aung San Suu Kyi.
Myanmar activists have reportedly planned more anti-coup rallies on Monday (Mar 15) in the commercial hub of Yangon.
Martial law was imposed in Hlaingthaya and in the Shwepyitha districts of Yangon, state media announced.
The Chinese embassy said several Chinese staff were injured and trapped in arson attacks by unidentified assailants on garment factories in Hlaingthaya, and that it had called on Myanmar to protect Chinese property and citizens.
As plumes of smoke rose from the industrial area, security forces opened fire on protesters in the suburb that is home to migrants from across the country, local media said.
Army-run Myawadday television said security forces acted after four garment factories and a fertilizer plant were set ablaze and about 2,000 people had stopped fire engines from reaching them.
Protests were planned for Monday in the country's second city of Mandalay, activist Myat Thu said, while residents in Yangon said demonstrations were planned in two areas of the city. Violence also broke out in other parts of Yangon as protests ran late into Sunday night.
The latest deaths would bring the toll from the protests to 126, the AAPP said. It said more than 2,150 people had been detained by Saturday. More than 300 have since been released.
MNA/PR