BEIJING — With surprising quickness, China dispatched some 20,000 troops to the region of Monday's deadly earthquake to help dig out the dead and injured.
Military planes and trucks ferried in another 30,000 reinforcements.
But the troops and civilian rescue workers were forced to struggle Tuesday against rainstorms and fog to reach thousands trapped under the rubble of schools, hospitals and residences. The death toll exceeded 13,000 Tuesday, state media said, and appeared certain to rise.
Prime Minister Wen Jiabao, who was on the scene directing rescue efforts, was seen bowing three times in a ritual of respect for the dead before the ruins of a collapsed school in the town of Dujiangyan, not far from the epicenter, the official news agency said. Wen declared that the soldiers, police and other rescuers should concentrate on clearing roads to reach those pinned under the rubble.
"We will save the people," Wen said through a bullhorn to survivors as he toured the disaster scene. "As long as the people are there, factories can be built into even better ones, and so can the towns and counties."
Wen flew in from Beijing soon after the scale of the disaster became apparent. His display of concern, and its swift reporting by the official media, was in marked contrast to the secretive way the Communist Party has handled emergencies in the past.
The toll of China's deadliest earthquake, a tremor at Tangshan in 1976 that killed about 240,000, was considered a state secret for years.
The rapid mobilization to Sichuan province reflected the priority that China's leadership places on delivering efficient disaster relief while showing the world it stands ready for anything that may come during the Olympics in August.
State media, often hesitant to report negative news, have been especially aggressive in covering the quake's aftermath, running pictures of bloody victims and grieving relatives. China Central Television provided virtually 24-hour coverage, dispatching reporters across a wide swath of the affected region.
The official New China News Agency reported that more than 18,000 were trapped under debris in Mianyang City. Another 2,000 people were found dead and 4,800 were missing in the little town of Mianzhu, near the quake's epicenter in Wenchuan county, the news agency reported.
On Tuesday, midafternoon aftershocks jarred Chengdu, the Sichuan provincial capital, sending thousands of office workers and residents into the streets.
An estimated 900 eighth- and ninth-grade students and their teachers were trapped in the Dujiangyan school where Wen paid his respects, officials told reporters.
Another school with up to 1,000 students and teachers inside collapsed in Mianyang, in Beichuan county, about 20 miles to the northeast, the state news agency said.
There was little prospect that many survivors would be found under the rubble. Only 58 people were extricated from demolished buildings across the quake area so far, China Seismological Bureau spokesman Zhang Hongwei told Xinhua news agency. In one county, 80 percent of the buildings were destroyed.
Rain was impeding efforts, and a group of paratroopers called off a rescue mission to the epicenter due to heavy storms, Xinhua reported.
But officials urged the public not to give up hope.
"Survivors can hold on for some time. Now it's not time to give up," Wang Zhenyao, disaster relief division director at the Ministry of Civil Affairs, told reporters in Beijing.
Thirty-one British tourists who were panda-watching in Wolong National Nature Reserve and initially were reported missing were safe and in the provincial capital of Chengdu on Tuesday night, the Chinese Foreign Ministry said in a statement.
Kerry Zobor, the U.S.-based spokeswoman for the World Wildlife Fund, said they have not been able to contact the 12 WWF members visiting the reserve or their tour operator.
"The communications are still disrupted, and we're hoping to have an update by the end of the day," Zobor said Tuesday.
All the pandas were reported safe.
Information from the Washington Post and Associated Press was used in this report.