ALMATY, Kazakhstan — Violent clashes broke out Friday between police and demonstrators in an oil town in western Kazakhstan where workers have been protesting for higher wages.

One witness said police opened fire on demonstrators meeting in the center of Zhanaozen, killing at least five people and wounding dozens.

Prosecutors confirmed that clashes had taken place and said at least two police officers had been injured, but denied reports of gunfire. Interior Ministry officials in the far western province of Mangystau could not be reached for comment.

The clashes appear to be some of the largest unrest to hit the energy-rich former Soviet nation since it gained independence in 1991.

Hundreds of workers at an oil facility controlled by the state-owned energy company KazMunaiGas in Zhanaozen have been protesting for better salaries and working conditions for more than six months. Almost 1,000 workers were fired in the summer for striking, but demonstrations have continued.

In a sign that Kazakhstan's authoritarian government may be attempting to contain information on developments in Zhanaozen, Internet users reported being unable to open independent news websites or Twitter.

Roza Teletayeva, who said she was a former oil worker dismissed in June for taking part in the strike, told The Associated Press that a meeting of several hundred demonstrators was surrounded by police Friday morning.

"We had no idea what was going to happen, we were just standing peacefully and doing nothing," she said.

Teletayeva said police opened fire on the crowd and that she had seen at least five people killed.

Footage broadcast by satellite channel K+ showed men in worker's outfits charging a stage erected in the town for the 20th anniversary of independence celebrations taking place Friday. A brief sound of gunfire is heard in the video, but it is unclear where it was being directed.

The General Prosecutor's Office said it was opening an investigation into who had provoked the unrest.

Authorities urged citizens in Zhanaozen to avoid crowded locations.