By Joe Cash and Ryan Woo

BEIJING (Reuters) - China has almost doubled its tally of injured in Tibet's deadly earthquake as rescuers widened a search on Friday for survivors in a remote county near the foothills of the Himalayas, despite dwindling hopes for survival.

The state-backed Global Times newspaper said the magnitude 6.8 quake had injured 337, for the first increase since Tuesday's initial estimate of 188, although the number of dead stayed at 126.

It is not yet clear how many are still missing, but more than three days later, experts say those trapped under the rubble are likely to have died of hypothermia.

Night-time temperatures in the region average from minus 10 degrees Celsius to minus 15 degrees C (14 degrees Fahrenheit to 5 degrees F), at this time of year, excluding wind chill.

More than 1,600 aftershocks had rocked the disaster zone by Friday, adding to the difficulty of moving more than 47,000 affected people to temporary shelters.

"Make sure no one is left behind!" was the headline of a report in the state-run Tibet Daily that said the top regional official of China's ruling Communist Party took action in less than half an hour after the quake.

Tibet's most serious disaster in years, the earthquake presents authorities with the challenge of quickly rescuing those still trapped, finding the bodies of the dead, and housing the tens of thousands displaced.

Its party secretary, Wang Junzheng, visited the hardest-hit villages in the quake epicentre in the county of Tingri.

"The elderly people held Wang Junzheng's hands, touched his forehead according to Tibetan customs, and shed tears," the paper said.

Many grassroots cadres, including local Tibetan officials, joined the relief effort to sift rubble and guard resettlement sites, even though their own homes collapsed, it added.

Xi met top ruling party officials to "study and arrange disaster relief," the official Xinhua news agency said.

"Efforts must be made to ensure a decisive victory in this tough battle," it quoted top leaders as saying, as they urged faster rebuilding and improvement in resilience.

Authorities must also find longer-term housing for the tens of thousands displaced, beyond warm tents, while ensuring a steady supply of daily necessities.

The government has sent 743,000 tonnes of items such as grain, cooking oil, meat and vegetables to the area, with the commerce ministry saying a further 2,000 tons of frozen pork and 1,600 tons of frozen beef and mutton are ready for delivery.

(Reporting by Joe Cash and Ryan Woo; Editing by Clarence Fernandez)