Chinese authorities were stepping up efforts to ensure drinking water and sanitation for the tens of thousands of people living without basic necessities since Monday's earthquake.

"We are sending 48 movable water-purifying machines to quake-hit areas, as airdropped bottled water is far from sufficient," Minister of Housing and Urban-Rural Development Jiang Weixin said Friday.

Two machines had already arrived in Chengdu and another six were expected to reach the Sichuan provincial capital on Friday night, he added.

Each machine could purify 30 to 50 tons of slightly polluted water, making a potable supply for 5,000 to 10,000 people every day, said Li Dongxu, head of the ministry's urban construction department.

In Sichuan alone, water supply facilities were severely damaged in about 20 cities and counties, and the situation was thought to be more serious in many other counties and townships, according to preliminary assessments.

The water supply networks in Chengdu, Mianyang and Guangyuan had been repaired for household supply, but supply was disrupted in Dujiangyan and Mianzhu as water pipes were damaged and could not be replaced quickly, though water plants were still working, according to Li.

However, people in hard-hit counties like Beichuan and Wenchuan were surviving on airdropped bottled water alone, as water supply facilities were destroyed, Li added.

The ministry was also shipping 800,000 water purification tablets to the quake zone, and 500,000 tablets arrived in Chengdu on Thursday morning.

A thousand household water purification sets were also arranged, with 700 to arrive at Chengdu on Saturday.