Turkey has declared three days of national mourning for victims of a coal mine explosion on Tuesday that killed at least 205 people and left hundreds more trapped underground, the prime minister's office said Wednesday.

The accident happened in a mine in the western province of Manisa, where a fire broke out following an explosion in a power distribution unit. Most of the victims died of carbon monoxide poisoning, said Minister of Energy Taner Yildiz.

The disaster occurred in the privately-owned mine in the district of Soma during a shift changeover. The fire broke out 150 meters underground, Yildiz said.

He said the accident could become "the worst disaster" in Turkish history, since hundreds more remain trapped underground.

Turkish President Abdullah Gul has cancelled an official visit to China, scheduled for May 15-21, over the disaster. Prime Minister Recep Tayyip Erdogan has also called off a trip to Albania.

Yildiz, the energy minister, said that 363 miners of the 787 who were working underground at the time of accident have been accounted for, including the deceased.

Rescue efforts continued throughout the night, but hopes of finding more survivors are diminishing.

The accident has sparked widespread anger as many denounced poor safety measures, accusing the government and mine companies of "negligence."

Mining accidents kill dozens of miners each year in Turkey.

The last major mining tragedy in Turkey occurred in 1992, when a fire and explosion killed 263 people. Two other mining accidents took place in 1983 and 1990, leaving 103 and 68 dead respectively.