More than five million buildings collapsed as a result of the earthquake
UN Secretary General Ban Ki-moon has praised China's "extraordinary leadership" in dealing with the recent earthquake in Sichuan.
He was speaking in the badly-hit town of Yingxiu, as Chinese Premier Wen Jiabao said the death toll had passed 60,000 and could rise to 80,000.
Mr Ban said the UN was ready to provide further support for the relief effort.
Earlier a Chinese official said 50 sources of radiation were now known to have been buried by the earthquake.
Thirty-five of the sources had been secured but the remaining 15 were buried under debris or in dangerous buildings, Environment Vice-Minister Wu Xiaoqing said.
Mr Wu said there had been no leaks of radioactive substances.
He did not specify the sources but experts say they probably came from hospitals, factories or research facilities, and not weapons.
Mr Ban was visiting China between trips to Burma, where is seeking to provide further relief for victims of Cyclone Nargis.
Later on Saturday he flew to Thailand where he opened a centre for cyclone relief supplies, ahead of an aid conference he is scheduled to attend in Rangoon on Sunday.
In Yingxiu, close to the Sichuan earthquake's epicentre, he paid tribute to Beijing's efforts.
"The Chinese government, at the early stage of this natural disaster, has invested strenuous effort and demonstrated extraordinary leadership," he said.
Ban Ki-moon tours quake-hit Yingxiu
The secretary general said people all over the world would stand beside the Chinese people and work together to deal with the disaster.
"If we work hard we can overcome this," he said, quoted by the Associated Press news agency.
"The whole world stands behind you and supports you."
More than five million people have been left homeless by the disaster.
On Friday, the vice-governor of Sichuan, the worst-hit province, Li Chengyun, appealed for more tents and set a three-year goal to rebuild towns and infrastructure in the region.
China's leaders have promised a 70bn yuan ($10bn; £5bn) reconstruction fund.
The government has also told Chinese banks to forgive debts owed by uninsured survivors to revive Sichuan's economy.
Meanwhile, concern is growing over a number of new lakes formed by the force of the earthquake.
Thirty-four lakes were created in the province when landslides blocked rivers, Xinhua news agency said.
Eight held more than three million cubic metres of water and one lake, less than 3km (two miles) from Beichuan town, had doubled in size in four days.
Officials are monitoring the lakes and have sent experts to assess them, the agency said.
Forecasters predict heavy rain in the region next week, which could further raise the water levels in the lakes.