Over 5,500 people have been rescued from under rubble following a devastating earthquake that hit southwest China three days ago, the Xinhua news agency said on Thursday.

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, killing around 15,000 people and devastating buildings and infrastructure.

"Over 5,500 people had been pulled out alive from under rubble by 8:00 a.m. [midnight GMT] on Thursday," the agency quoted a police source as saying.

Some 25,000 people are believed to still be trapped under collapsed buildings.

The epicenter of the quake was located some 60 miles (96 km) northwest of Sichuan's provincial capital, Chengdu, where more than 14,000 people have been reported dead. Authorities fear that the death toll could rise and the national meteorological center is warning that more tremors could strike the country.

More than 9 million people have been evacuated from the affected areas. The earthquake damaged power plants, electricity and communication lines, and also destroyed two chemical plants in the Sichuan province, burying hundreds of workers and spilling more than 80 tons of toxic liquid ammonia.

An estimated 100,000 Chinese troops are involved in the ongoing relief operation. Rescue workers are currently only able to reach areas close to the epicenter by air and water.

The earthquake struck on Monday at 2:28 p.m. local time (06:28 a.m. 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.