Myanmar police fired water cannon and tear gas at protesters against a Chinese-backed copper mine Thursday, the government said, injuring dozens in a crackdown hours before Aung San Suu Kyi visited the area.

The demonstration was the latest example of long-oppressed Myanmar citizens testing the limits of their new freedoms after the end last year of decades of authoritarian junta rule that saw protests routinely stamped out.

Demonstrators, who say farmers have been evicted to make way for the mine near the town of Monywa in northern Myanmar, recounted being shaken from their sleep in the early hours of the morning as police moved in to disperse them.

Several monks were arrested and around 30 others "suffered burns to their body", a monk called Yaywata, who goes by one name, told AFP.

It was unclear exactly what kind of device caused the burns.

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

"It's not true at all that chemical weapons were used in the crackdown," Nyan Tun, a director of the presidential office, told AFP.

As criticism of the police mounted, opposition leader Suu Kyi arrived in the area where she met officials from the Chinese mine operator Wanbao near the scene of the crackdown and later delivered a speech linked to the dispute.

In her public address, Suu Kyi "promised to try her best to find a peaceful solution" to the mine row and to look into how the crackdown happened, according to her spokesman Ohn Kyaing.

Villagers, monks and students had been warned to vacate protest camps near the mine -- a joint venture between Wanbao and military-owned Myanmar Economic Holdings -- by Tuesday, but had vowed to defy authorities.

The government is being closely watched, with activists warning that the use of junta-style security tactics could undermine Myanmar's reform process.

"These kind of old habit solutions should not happen," said Kyaw Min Yu, a member of the '88 Generation movement, born during huge student-led demonstrations in 1988.

"The government should be more patient in this transition period. If it (violence) is again used in the future, we cannot continue forward."

Protesters are demanding work is stopped until environmental and social impact studies are carried out.

During a September protest activists said 8,000 acres (3,200 hectares) of land had been confiscated from local farmers without consultation, and in some cases without compensation.

Chinese-backed projects to tap Myanmar's abundant natural resources have sparked resentment among residents, who have been testing the new reformist government's proclaimed tolerance of freedom of expression.

An editorial in Chinese state newspaper Global Times said the protesters were standing in the way of development. "It will be a lose-lose situation for China and Myanmar if the project is halted," the editorial said.

The mine demonstration echoes fierce opposition to a Chinese-backed mega-dam which saw Thein Sein order the scheme's suspension last year in response to public anger.

The former general's government earlier this year approved a bill allowing authorised peaceful protests but demonstrators must seek permission five days in advance.

Several demonstrators in Yangon were charged Tuesday with defaming the state after they called for a halt to the project.