ZHOUQU China (Reuters) - Chen Daochen knows he will never see his father or elder brother alive again. Yet still he digs through the thick yellow mud that cascaded through their home, killing four members of his family.

"I know they're dead. But I have to get them out. I have to see them with my own eyes or I won't know for sure," he said quietly, desperately pulling rolls of plastic pipes from the simple brick house to get at the bodies.

"At least the kids were not at home when it happened," Chen added numbly, a pile of damp school books at his feet slowly rotting in the damp heat.

It is a scene of stunned grief repeated across Zhouqu, a remote town in northwestern Gansu province. At least 702 people died when a mass of mud and rocks swept down on sleeping residents at the weekend. Another 1,042 are missing.

Rescuers who have swarmed into Zhouqu are not giving up hope of finding anyone else alive, but they warn that chances are slim in the chocking mud, so thick in places it has piled up to what used to be the third or fourth floor of buildings.

Logs and stones have been laid over the sludge to ease access. They seem almost to float when stepped on, threatening to give way, and plunge rescuers into the morass.

"It's different from an earthquake. With all this mud it gets into every corner of a room. You drown," said Dan Xiaoli, a rescue worker from next-door Sichuan province, where tens of thousands died in a devastating earthquake two years ago.

"But we need to keep looking in case there is a miracle," she added, dressed in orange overalls and carrying a first aid kit.

Close by, a crowd gathers expectantly, peering down to where troops have pried open a small hole in what was the roof of a house, using their hands, a few shovels and some sledgehammers.

"Keep quiet! Step back! We can hear someone in there!" shouts one soldier. A reverent hush falls, and people edge back.

Five minutes later, the silence becomes sobs as the pale white arm of a dead man pokes through the rubble. Even the most curious of bystanders recoil from the smell.

Two women collapse wailing, unable to stand their grief, and are carried off by relatives. Almost everyone has a tragic story to tell. Many escaped by luck alone.

"The first to fourth floors of my building were swamped. We were on the sixth. Dozens of my neighbors are still in the mud. We've had to give up trying to get their bodies out," said Liu Jiesheng, 40, his eyes bloodshot from lack of sleep.

While relief supplies and workers continue to arrive, poor roads and the area's remoteness are hampering efforts.

The nearest airport is a seven-hour drive away, mountains tower over settlements in the valleys, and on the main artery from the south, traffic has to be strictly limited.

"The road is too narrow. We have to control what goes up there or there will be chaos and everything will get blocked," said one policeman, after a brief argument with some officials from Sichuan trying to bring in bottled water.

Yet despite the tough restrictions, much heavy lifting equipment sits idle, unable to either get into the town or be used in large parts of it, lest it slip into the mud.

"The government is doing what it can. But we are a long way from anywhere here. This is not a problem that will be solved overnight," said resident Wang Xuezhen, who lost four family members and survived only because he was away for the night.

(Editing by Emma Graham-Harrison and Ken Wills)