YANGON: Myanmar's anti-coup protesters returned to the streets in force on Wednesday with the biggest demonstrations since troops fanned out around the country to quell opposition to the new military junta.

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, with protesters blockading roads with vehicles to stop security forces from moving around the nation's biggest city.

"We have to fight until the end," Nilar, a 21-year-old student who asked not to use her real name, told AFP.

"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 more violent efforts by the regime to bring resistance to heel, 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 on the weekend.

But social media platforms were 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 highlands region of Chin state to a small town in the Irrawaddy delta that saw a parade of protesters hoisting Suu Kyi posters.

Right outside the capital Naypyidaw, tens of thousands of people from different sectors -- including engineers, doctor, and teachers -- marched through the logging town of Pyinmana carrying signs saying "Help Myanmar".

UN special rapporteur Tom Andrews warned that reports of soldiers being brought into Yangon 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.

There were no signs of a major troop mobilisation in Yangon on Wednesday morning.

In recent days, rubber bullets, tear gas and even slingshots have been used against protesters.

One young woman remains in a critical condition in Naypyidaw after being shot in the head last week.

The military said a police officer had died in Mandalay after a confrontation with protesters on Sunday.

"Those who committed lawless action on the police officer will be dealt with as necessary," an army statement said.

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 for possessing unregistered walkie-talkies found in her home.

Her lawyer Khin Maung Zaw told AFP on Tuesday she was also charged with violating the country's disaster management law. Further details of that charge have not been made public.

The disaster management law has also been used against deposed president Win Myint for an election campaign event that the junta claims broke coronavirus restrictions.

Her lawyer added that Suu Kyi and Win Myint, both of whom he has yet to have any contact with, were expected to appear via video link during a March 1 trial.

Suu Kyi had already made an appearance in court via video conference Tuesday, without his presence, he said.

UN rapporteur Andrews described the court proceedings as a "secretive trial".

Military spokesman Zaw Min Tun said Tuesday that both Suu Kyi and Win Myint were in a "safer place" and "in good health".

"It's not like they were arrested -- they are staying at their houses," the general told a press conference.

More than 450 people have been arrested since the coup, according to the Assistance Association for Political Prisoners monitoring group.

Western powers and the United Nations have repeatedly condemned the leaders of Myanmar's new military administration, which insists it took power lawfully.

China had initially not criticised the coup, which Chinese state media described as a "cabinet reshuffle".

However, Beijing's ambassador to Myanmar said Tuesday that the current situation in the country was "absolutely not what China wants to see".