Several demonstrators have been injured after Burmese security forces launched a crackdown against protesters who've been occupying part of a Chinese owned copper mine.

Authorities said that riot police used tear gas and water cannon to break up the protest against the expansion of a copper mine near the north western town of Monywa.

Activists said that incendiary devices, such as phosphorous bombs, were thrown into the protest camps, injuring at least 50 people.

President Thein Sein's office said that water cannon, tear gas and smoke bombs were used against the protesters but a spokesman denied allegations a form of chemical weapon had been deployed.

Mr Nyan Tun director of the presidential office said that "It's not true at all that chemical weapons were used in the crackdown."

For months, thousands of locals have been protesting against the expansion of the mine which they fear would damage the environment. They've also accused Burmese authorities of forcibly evicting residents and confiscating almost 8,000 acres of land.

Villagers, monks and students had been warned to vacate protest camps near the mine by Tuesday but had vowed to defy authorities. The crackdown came as Opposition Leader Ms Aung San Suu Kyi visited the area calling for a peaceful solution.

She said that "I want to solve this problem peacefully and in a dignified manner. I want to request that all of you help me on this."

She said that she had met company officials and hoped to broker a peace. I'd like to meet with the respective villagers and those who are opposing this project and mediate between the two sides. I would like to ask the people to cooperate with patience."

The copper mine, Burma's biggest is run by a unit of China North Industries Corp under a deal signed in June 2010. It is backed by the military owned Union of Myanmar Economic Holdings Limited which operated extensively under the military regime that ruled for almost half a century until 2011.