'We have no idea when we will find them, we just keep digging. But it's unlikely that they are still alive, as it's just been too long [since they were buried],' he said.

Mr Zhang said that of the 24 trapped, 12 were male and they came from eight households. Eight were children and one was elderly.

Xinhua reported that 20 bulldozers, trucks and excavators were being used in the rescue operation.

Another county government official, surnamed Zhang, said that in view of possible further landslides, about 60 households in the village had been relocated.

'It's still unclear if the relocation will be temporary. If an environmental assessment shows the cave houses are safe, they can move back,' he said.

Mr Zhang said provincial authorities were investigating the cause of the cave-in. Xinhua quoted county officials as saying the accident was a 'serious geological disaster' set off by a 'natural collapse of the loess slope'.

In a notice circulated after the landslide, the provincial government urged local authorities to guard against natural disasters as the province had entered a flooding season, Xinhua reported.

It said special attention should be paid to houses under the loess slopes.

Cave houses, constructed by digging caves in the earth cliffs, are popular residences on the loess plateau as they require little technology and are insulated from the extremes of heat and cold.

The loess plateau, situated on the upper reaches of the Yellow River, has seen serious soil erosion in recent decades.