BEIJING, Nov 24 (Reuters) - The bodies of 31 victims of a landslide in central China are so badly crushed that DNA samples may be needed to identify them, state media reported on Saturday.

A long-distance bus was buried under an avalanche of boulders, earth and mud at the entrance to a railway tunnel being built in Hubei province near China's massive Three Gorges Dam.

Rescuers had recovered all but one of the bodies by Saturday, four days after the landslide, Xinhua news agency reported. A spokesman with the Badong county government said they were nearly all badly disfigured.

The long-distance coach from Shanghai was crowded with returning migrant workers. Thirteen of the victims were from five families, including a four-month-old boy, his 20-year-old mother and two one-year-old boys, according to a partial list of the passengers posted on Badong government's Web site.

Zhang Cunyuan, 46, was taking his wife and son home to his village to celebrate his father's 70th birthday.

"I called him at around 8 a.m. on Tuesday morning and he told me they would arrive soon," the father, Zhang Xiuming, told reporters. The phone abruptly went dead and Zhang was unable to get through to his son again, Xinhua reported.

Some boulders dislodged by the slide were so big that rescuers had to blow them up to reach the bus, which was finally found on Friday.

The landslide struck near a tributary of the 660-km (410-mile) Three Gorges Dam reservoir.

Reports of the disaster have not speculated on whether the slide could be linked to the dam's rising waters, which are due to peak at 175 metres (574 feet) above sea level next year.

But local residents are concerned by what they say has been an increase in landslides and tremors since the water level rose last year, putting pressure on steep brittle slopes in places like Badong.

In September, dam officials warned of potential "environmental catastrophe" unless erosion and geological instability around the reservoir were controlled -- an abrupt departure from bright propaganda about the world's biggest dam.

Since then they have repeatedly said those threats are being dealt with and the dam's environment is better than expected.

"There have been no injuries or deaths" due to dam-related landslides, Tong Chongde, a spokesman for the Three Gorges Project Construction Committee, told a news briefing on Thursday. On Friday, Tong said he had not heard of the bus deaths. (Reporting by Alan Wheatley and Chris Buckley; editing by John Chalmers)

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