(Updates death toll, adds Chinese comment, martial law in suburb)

* Two Chinese factories reported set ablaze

* China's embassy says Myanmar must stop violence

* State television says one policeman killed

March 14 (Reuters) - Security forces killed at least 14 protesters in a poor, industrial suburb of Myanmar's main city on Sunday and at least three people in other parts of the country, according to local media.

State television said a policeman had also been killed in one of the bloodiest days of protests against the Feb. 1 coup.

China's embassy called on Myanmar to protect its property and citizens after saying two Chinese-financed garment factories were set ablaze by unknown attackers.

Protests are now in their sixth week since the coup toppled elected leader Aung San Suu Kyi and plunged the Southeast Asian country into turmoil, with the economy paralysed by strikes by opponents of the army takeover.

Security forces opened fire on protesters in the Hlaingthaya district of the city, a poor suburb that is home to migrants from across the country, domestic media said. Plumes of black smoke rose over the area.

Myanmar Now said at least 14 protesters had been killed, according to the local hospital and a rescue worker.

"An official from Hlaingthaya Hospital said the death toll and wounded were still arriving," its report said. Other Myanmar media gave even higher tolls in the area.

State television MRTV said martial law had been imposed in the district. A junta spokesman did not answer calls requesting comment.

Doctor Sasa, a representative of elected lawmakers from the assembly that was ousted by the army, voiced solidarity with the people of the district.

"The perpetrators, attackers, enemies of the people of Myanmar, the evil SAC (State Administrative Council) will be held accountable for every drops of blood that shed," he said in a message.

CHINA SAYS FACTORIES BURNED

Myanmar Now quoted residents as saying three factories were set ablaze in Hlaingthaya. It was unclear whether those included two Chinese-financed garment factories that Chinese state news service CGTN said were burned.

CGTN quoted the Chinese embassy in Myanmar as having called for assistance.

"China urges Myanmar to take further effective measures to stop all acts of violence, punish the perpetrators in accordance with the law and ensure the safety of life and property of Chinese companies and personnel in Myanmar," the statement said.

It said the perpetrators had not been identified.

Opponents of the coup have criticised China for not coming out more strongly against the army takeover as Western countries have done. China has said that the priority is stability and that it is Myanmar's internal affair.