A methane gas explosion ripped through a coal mine in western Turkey Thursday evening, killing at least nine miners and trapping several others, authorities said.

Gov. Selahattin Hatipoglu said at least nine were killed after the blast caused a shaft to collapse at the mine in the village of Odakoy in western Balikesir province, the semiofficial Anatolia news agency reported.

CountryWatch: Turkey

Several other miners were still believed trapped inside the mine, but the exact number was not clear.

Seven miners who were participating in rescue efforts were hospitalized with methane gas poisoning, private NTV television said.

The explosion took place nearly 500 feet below ground, Anatolia quoted Erhan Otakoylu, the owner of the private coal mine, as saying. The site is located some 300 miles south of Istanbul, Turkey's largest city.

A military helicopter was transferring workers from nearby mines to help the rescue effort, Anatolia said.

Accidents are not uncommon in Turkish mines — a result of safety violations, outdated equipment and high concentrations of methane gas.

Last June, six coal miners died of methane gas poisoning when a shaft collapsed near the Black Sea port of Zonguldak. A methane gas explosion in April 2005 killed 18 people at another coal mine in the town of Gediz in western Kutahya province.

Turkey's worst mining disaster was in 1992, when a gas explosion killed 270 workers near Zonguldak.