The toll from the deadliest quake to hit China in three decades crossed 12,000 on Tuesday and may go up further with thousands remaining buried under rubble or missing and army and rescuers racing against time to reach remote towns and villages devastated by the disaster.
Thousands of Chinese troops and medical teams have been dispatched to the worst-affected Sichuan province.
The Sichuan provincial seismological bureau said more than 1,180 aftershocks up to magnitude six on the Richter scale have been recorded as of 5 am (local time) on Tuesday.
Chinese state media reported that the toll now exceeds 12,000 in Sichuan province alone.
At least 10,000 people remained buried in Mianzhu city in the province while 3,629 people had been confirmed dead and 18,645 were still buried under debris in Mianyang city.
The official Xinhua news agency said there was serious damage to the buildings and roads in Mianyang and that water and gas supplies had been cut off. Premier Wen Jiabao, who flew to Sichuan on Monday evening, said the situation in the quake-hit area was worse than previously feared.
"The situation is worse than we previously estimated and we need more people here to help," Wen said at the disaster relief headquarters in Dujiangyan, 100 km from the quake's epicentre.
"Judging from the current situation, we cannot just rely on medical teams inside Sichuan province, we need teams to come in from outside," Wen was quoted as saying on state-run China Central Television.
"People are trapped in debris. We must use every second," Wen said.
Hampered by rain, blocked roads and broken telecommunication networks, rescuers dug through rubble of toppled schools, factories and houses as they struggled to reach the worst-hit areas near the epicentre.
Attempts to reach Wenchuan County -- the quake epicentre -- through land, air and water were put paid to by rain, and paralysed transport and communications, state media reported, as the government accelerated its relief efforts, rushing more troops and relief teams.
Another 34,000 troops were advanced towards the disaster-struck regions by plane, train, road and even foot, in addition to 16,760 soldiers already immersed in disaster relief efforts.
In Beichuan County, about 160 km northeast of the epicentre, rescuers were searching frantically for survivors in the debris under which at least 1,000 students and teachers were buried when a school in the county collapsed.
A strong aftershock measuring 6.1 on the Richter scale rocked Sichuan province in the afternoon, with epicentre again in Wenchuan County, an official with the China Seismological Bureau said.
This was the strongest aftershock after the devastating quake, measuring 7.8 on the Richter scale, which was felt within a radius of 200 km, it said.
"Although more than 24 hours have passed since the earthquake, there is still hope for survivors," Wang Zhenyao, Director in charge of the disaster relief with the Ministry of Civil Affairs said.
"We will never give up rescue operations so long as the slimmest hope of survival exists".
The government has earmarked 360 million yuan ($52.17 million) for disaster relief, as several nations, including the US and Japan offered aid to China in its relief efforts.
Foreign Ministry spokesman Qin Gang said China was ready to accept the offer.
"Many countries and international organisations have expressed their 'will' to provide various kinds of aid to China. We express our thanks and welcome (it) in this regard."
Quoting the Sichuan provincial emergency management office, Xinhua said 2,000 tourists, including a group of about 15 British tourists, were 'out of reach' in Wenchuan.
The Foreign Ministry spokesman said no casualties had been reported among the foreigners.
"According to our information now, there are no dead or injured people (among foreigners)," Qin said.
The earthquake will not affect preparations of the Beijing Olympic Games, an official said. Beijing Olympic Media Centre Director Li Zhanjun said the earthquake stricken area 'is not on the route of the torch relay. So, the relay will go on as scheduled'.