The Chinese Government rushed 2,000 troops to a dam above the devastated town of Dujiangyan, in Sichuan province, today in an emergency attempt to plug cracks caused by the earthquake.

If the Zipingpu Dam were to collapse, torrents of water would surge downriver into some of the areas where more than 42,000 people are reported dead or missing.

Rescuers finally reached some the worst hit of those areas in the Sichuan province today. The official death toll now stands at 14,866, but while the army and emergency workers battle to reach isolated areas and scour mile after mile of rubble, the scale of the disaster continues to rise.

Li Chengyun, the vice governor of Sichuan, told the official Xinhua news agency that almost 26,000 people were buried in collapsed buildings and a further 1,451 were missing in his province alone.

Damage done to roads and communication lines meant that soldiers arrived in Wenchuan county, the epicentre of the quake, for the first time today after a two-day hike through the ravaged region.

When they reached the city of Yingxiu, rescuers found it "much worse than expected". Of the town’s population of about 10,000, it is thought that only 2,300 survived and 1,000 of those were badly hurt.

Troops have been sent to the Zipingpu Dam to ensure that further infrastructure collapse does not leave the region engulfed in water just as officials had begun to re-open some of transport routes.

He Biao, the director of the Aba Disaster Relief headquarters, said: "Currently, the most dangerous problems are several reservoirs near Wenchuan."

"There are already serious problems with the Tulong Reservoir on the Min River. It may collapse. If that happens, it would affect several power plants below and be extremely dangerous," he said, according to transcripts released on the CCTV website.

A senior engineer, however, told Times Online that the Zipingpu Dam had suffered surface cracks but was not in immediate danger of collapse.

The National Development Reform Commission, China’s top economic planning body, announced that the earthquake had damaged 391 dams overall, but most of those were small.

The driving rain that halted helicopter flights until now has eased, allowing military helicopters to drop food and medicine to survivors in remote mountain villages.

Troops were still working to clear blocked roads and train tracks today after collapsed tunnels and landslides rendered them impassable.

Makeshift aid stations and refugee centres were also springing up over a disaster area the size of Belgium.

As rescuers entered the most isolated areas of Sichuan, people were still being pulled from the rubble alive.

One of the survivors was Zhang Xiaoyan, 34, who was eight months pregnant. She was successfully extricated from debris after 50 hours beneath the surface in Dujiangyan.

"It’s a miracle brought about by us all working together," said Sun Guoli, fire chief of the nearby provincial capital Chengdu, who supervised the rescue.

The disaster has been reported extensively by the Chinese media, with state-run television providing 24 hour news coverage. During previous crises, Beijing has been accused of attempting to cover-up the scale of the problems.

Wen Jiabao, the premier, has been on a high-profile tour of the affected area. Today he was present when a three-year-old girl was rescued after more than 40 hours under the bodies of her parents in rubble in the Beichuan region.

Rescuers found Song Xinyi yesterday but were unable to pull her out due to fears the debris above her would collapse. She was fed and shielded from the rain until rescuers released her from the rubble.

The premier said that 100,000 troops and police had been dispatched to the disaster zone as he visited a school in Beichuan, where two classroom buildings collapsed causing "heavy casualties".

"The party and the government are concerned about you. Your pain is our pain," Wen told survivors in Red Cross tents with his arms wrapped around two little girls in footage aired on CCTV.

Rescuers have yet to find at least 19 British holidaymakers who were travelling on a coach tour in Wenchuan when the earthquake struck.

"All lines of communication to the region are still down and as such no further information is known at this time," said a spokesman for Kuoni Travel which arranged the tour.

"We are working closely with the British Consulate in China."

The Foreign Office said it has so far had no reports of any British casualties, but officials are attempting to make contact with "a number" of missing people.