The quake, measuring 7.8 on the Richter scale, was the worst to hit the country in more than three decades, and affected eight provinces, devastating buildings and infrastructure. Almost 30,000 people are still believed to be buried under rubble.
Some 94,000 people are said to be unaccounted for near the epicenter of the quake, which was located some 60 miles (96 km) northwest of Sichuan's provincial capital, Chengdu. Deaths have also been reported in neighboring provinces.
More than 9 million people have been evacuated from the affected areas. Authorities fear that the death toll could rise and the national meteorological center is warning that more tremors could strike the country.
The earthquake damaged power plants, electricity and communication lines, and also destroyed two chemical plants in the province, burying hundreds of workers and spilling more than 80 tons of toxic liquid ammonia.
Local officials denied rumors on Wednesday that water sources in Dujiangyan, in the Sichuan province, had been cut due to contamination from chemical plants, the Xinhua agency said.
The earthquake struck on Monday at 2:28 p.m. local time (06:28 GMT). Tremors were also felt some 930 miles (1,500 km) away in the capital, Beijing, where office workers rushed out into the streets as their buildings shook.
An estimated 100,000 Chinese troops are involved in the ongoing relief operation. The government has allocated a total of $125 million in emergency aid for the quake-hit areas.
Russia's new president, Dmitry Medvedev, sent a message to China's leader Hu Jintao with an offer of assistance in relief operations following the disaster.
The first plane with 30 metric tons of the Russian humanitarian aid, including tents, mattresses and blankets, landed in Chengdu at 11.00 a.m. Moscow time (07:00 GMT) on Wednesday.
The Russian Ministry for Emergency Situations said Russia was ready to send another three aircraft with humanitarian aid, a rescue team and a mobile hospital to China to assist in the relief operation if a request was made by the Chinese authorities.
A leading insurance research firm, AIR Worldwide, said the damage from the China earthquake is likely to exceed $20 billion.