Myanmar security forces killed at least 38 people in a single day, 22 of them in the Hlaingtharyar district of Yangon, the Assistance Association for Political Prisoners advocacy group said.

Myanmar state television said that martial law had been imposed in Yangon's Hlaingthaya district.

Earlier, a civilian leader of the government in hiding vowed to continue supporting a "revolution" to end the military coup in Myanmar. 

A video showed protesters holding handmade shields and wearing helmets as they confronted security forces in Yangon's Hlaingtharyar district. 

Plumes of black smoke rose over the area and one report said two factories in the district had been set on fire.

The violence comes a day after the acting leader of Myanmar's parallel civilian government said it will seek to give people the legal right to defend themselves as the death toll in protests against last month's coup exceeded 80. 

'The dawn is close'

Mahn Win Khaing Than, who is on the run along with most senior officials from the ruling National League for Democracy Party, addressed the public via Facebook late on Saturday, saying, "This is the darkest moment of the nation and the moment that the dawn is close".

He said the civilian government will "attempt to legislate the required laws so that the people have the right to defend themselves" against the military crackdown.

Mahn Win Khaing Than was appointed last week as acting vice-president by representatives of Myanmar's ousted lawmakers, the Committee for Representing Pyidaungsu Hluttaw (CRPH), which is pushing for recognition as the rightful government.

It has announced its intention to create a federal democracy and leaders have been meeting representatives of Myanmar's largest ethnic armed organisations, which already control vast swathes of territory across the country. 

Some have pledged their support.

"In order to form a federal democracy, which all ethnic brothers, who have been suffering various kinds of oppressions from the dictatorship for decades, really desired, this revolution is the chance for us to put our efforts together," Mahn Win Khaing Than said.

His address was greeted with thousands of approving comments from many who followed it on Facebook. "Keep it up Mr President! You are our hope. We are all with you," wrote one user, Ko Shan.

The junta, which could not be reached for comment on Saturday, has declared CRPH illegal and said anyone involved with it could be charged with treason, which carries the death penalty.

The CRPH has declared the junta a "terrorist organisation".

READ MORE:Death toll of crackdown on Myanmar's anti-coup protesters continues to rise

13 killed in bloodiest day 

More than 80 people had been killed as of Saturday in widespread protests against the military's seizure of power, the Assistance Association for Political Prisoners advocacy group said. 

Over 2,100 people have been arrested, it said.

At least 13 people were killed on Saturday, one of the bloodiest days since the February 1 coup, witnesses and domestic media said.

Five people were shot dead and several injured when police opened fire on a sit-in protest in Mandalay, Myanmar's second-biggest city, witnesses told Reuters.

Two people were killed in the central town of Pyay and two died in police firing in the commercial capital Yangon, where three were also killed overnight, domestic media reported.

"They are acting like they are in a war zone, with unarmed people," said Mandalay-based activist Myat Thu.

He said the dead included a 13-year-old child.

Si Thu Tun, another protester, said he saw two people shot, including a Buddhist monk. "One of them was hit in the pubic bone, another was shot to death terribly," he said.

A truck driver in Chauk, a town in the central Magwe Region, died after being shot in the chest by police, a family friend said.

A spokesman for the junta did not answer phone calls from Reuters seeking comment. Junta-run media MRTV's evening news broadcast labelled the protesters "criminals" but did not elaborate.

READ MORE: Myanmar forces surround protesting rail workers as UN fails to condemn coup

Protests against 8-8-88 campaign

Saturday's protests erupted after posters spread on social media urging people to mark the death anniversary of Phone Maw, who was shot and killed by security forces in 1988 inside what was then known as the Rangoon Institute of Technology campus.

His shooting and that of another student who died a few weeks later sparked widespread protests against the military government known as the 8-8-88 campaign, because they peaked in August that year. An estimated 3,000 people were killed when the army crushed the uprising.

Aung San Suu Kyi emerged as a democracy icon during the movement and was kept under house arrest for nearly two decades.

She was released in 2010 as the military began democratic reforms. 

Her National League for Democracy won elections in 2015 and again in November last year.

This year, the generals overthrew her government and detained Suu Kyi and many of her cabinet colleagues, claiming fraud in the November elections.

READ MORE: Explained: the coup in Myanmar and its political ramifications