Much of the country has been in open revolt since the military deposed Nobel laureate Aung San Suu Kyi’s government at the start of the month and charged her under an obscure import law.
Tens of thousands rallied in Yangon, some blockading roads with vehicles to stop security forces from moving around the nation’s biggest city.
Police and soldiers were spotted near a key protest junction but appeared to be hanging back, looking on as demonstrators streamed past.
“We have to fight until the end,” Nilar, a 21-year-old student who asked not to use her real name, said.
“We need to show our unity and strength to end military rule. People need to come out on the streets.”
Wednesday’s crowds came in defiance of violent efforts by the regime to bring resistance to heel — including use of tear gas and rubber bullets — following nationwide street protests and a disobedience campaign encouraging civil servants to strike.
Demonstrations over the past two days had been noticeably smaller since troops were deployed around Yangon at the weekend.
But social media platforms had been flooded with calls for a show of force by protesters in the hours before the junta imposed a third consecutive overnight internet blackout.
By noon, there were anti-coup demonstrations across Myanmar, from the remote highland region of Chin state to a small town in the Irrawaddy delta.
Right outside the administrative capital Naypyidaw, tens of thousands of people from different sectors marched through the logging town of Pyinmana carrying signs saying “Help Myanmar”.
UN special rapporteur Tom Andrews warned that soldiers going into Yangon, as had been reported, could lead to the situation there spiralling out of control.
“We could be on the precipice of the military committing even greater crimes against the people of Myanmar,” he said.
Meanwhile, the military justified its power seizure by alleging widespread voter fraud in November elections won by Suu Kyi’s party in a landslide.
After her detention in a dawn raid on February 1, Suu Kyi was charged with possessing unregistered walkie-talkies found in her home.