GUIYANG, May 8 (Xinhua) -- The death toll from Monday's bus accident in southwest China's Guizhou Province has risen to 18 and six remain in critical condition in hospital list, local traffic police said on Tuesday.

The coach plunged off a highway into a valley at least 80 meters deep in Qianxi County of Bijie Prefecture, western Guizhou, at around 5:30 a.m. on Monday.

Seventeen people died at the scene and another in hospital early on Tuesday, said Yuan Baoping, an officer with the traffic police authorities in Bijie.

Twenty-four people were injured in the accident, six of whom were in intensive care, he said.

The victims were all peasants from Zhenxiong county in Zhaotong, a city in the neighboring Yunnan Province. They were on their way home from Jinhua, an industrial city in the rich eastern province of Zhejiang, where they worked as migrants.

Three children were among the dead, while two of the injured were pregnant.

A preliminary investigation attributed the cause of the accident to driver fatigue as the bus had traveled a long way from Zhejiang and the weather was clear, said Yuan.

Liao Dexiang, the driver with 18 years experience, survived with a severe leg fractures.

The accident occurred on the last day of the seven-day May Day holiday, which started on May 1.

Figures released by the State Council Work Safety Committee on Sunday showed 75 people died in 33 accidents in the first four days of the holiday.

In another road accident in southwest China, a light truck ploughed into a crowd of people waiting for a bus in Yunnan Province on Friday, killing 16.

A coal mine explosion the following day claimed 28 lives, with two others still missing in the northern Shanxi Province.