A woman protesting against a controversial Chinese-backed copper mine in Myanmar has been shot dead, a government spokesman said Tuesday, announcing an investigation into how police handled the latest clash at the site.

The woman, believed to be in her 50s, was gunned down Monday when police opened fire as local protesters tried to stop workers from erecting fences near Letpadaung mine in the northwestern town of Monywa.

"We see it as a sad moment because a woman died during this conflict," information minister Ye Htut told AFP.

He said police had opened fire but did not immediately confirm that their bullets killed the woman.

The minister said he believed some protesters had used slingshots to attack workers at the mine and had briefly detained 10 members of staff.

"We will review how the police handled (the clash)," Ye Htut said.

State media reported Monday that nine protesters and 11 police officers had also been injured during the protest.

The mine has triggered fierce opposition from local villagers due to alleged land grabs and environmental damage. It has raised questions about Myanmar's reliance on investment from neighbouring China -- which gave crucial political support to the former junta.

China's Wanbao, which runs the project as part of a joint venture with a major Myanmar military conglomerate, said the woman's "senseless death" was "painful and poignant".

"The events leading up to her death are still unclear. We understand the police were also at the scene, and we hope they will start investigating this tragic event," the company said in a statement on its website.

Wanbao said it had completed two major consultations this year in a process of "reconciliation" with local people.

In November 2012 a botched police raid using phosphorus on a protest at the mine left dozens of people, including monks, with burn injuries.

That crackdown, the harshest since the end of outright army rule in 2011, sparked fury in the Buddhist-majority country.

Earlier this year two Chinese workers were kidnapped at the site by activists, though they were later released unharmed.

A new quasi-civilian government has implemented headline-grabbing reforms in recent years, including releasing political prisoners and allowing opposition leader Aung San Suu Kyi into parliament.

But serious challenges remain, particularly widespread land disputes.

Wanbao on Monday said Myanmar would receive $140 million a year in tax from the project.

In July 2013 the country revised the terms of the mine deal with Wanbao, giving the nation a share of the profits in an apparent attempt to allay public anger.

Suu Kyi was heckled by villagers last year after she recommended that the mine be allowed to go ahead.