At least 221 people were killed and more than 1,400 injured by a strong earthquake that jolted Southwest China's Yunnan province on Sunday afternoon.

The 6.5-magnitude quake hit at 4:30 pm on Sunday, with the epicenter in Zhaotong city.

Earthquake experts said it was the highest-magnitude earthquake to hit the province in the past 18 years.

By 8 pm Sunday, the quake had toppled more than 12,000 houses, and traffic, electricity and telecommunications in the area had been interrupted.

President Xi Jinping urged an all-out effort to save as many people as possible. Premier Li Keqiang called on officials from eight ministries to build a rescue command group in Ludian county.

Many rescuers, as well as disaster relief materials, have been rushed to the county.

The China International Search and Rescue Team has dispatched 100 rescuers and 12 dogs, while 200 soldiers from the provincial command were on their way to the epicenter.

Yu Yang, commander of reserve forces in the province, said they had prepared 500 rescue devices within one hour of the quake.

More than 2,500 officers and soldiers have been dispatched to join the disaster relief operation.

The provincial commission for disaster reduction said it had provided 2,000 tents, 3,000 folding beds, 3,000 quilts and 3,000 cotton-padded clothes.

But mud-rock flows damaged roads to the county, so rescuers had to enter the county on foot.

Hong Fengzhong, director of the disaster relief department of the Red Cross Society of China, said that the first team of four from the society was on the way with relief supplies including tents, quilts and coats.

"Frequent landslides have made the mountain road even bumpier, and we could only drive about 30 km/h in the rain," Hong told China Daily.

The temperature at the epicenter had fallen below 10 C and "the people there need tents most," he said.

Shi Wen'e, a native of the city, told China Daily that she felt strong shaking as the disaster happened, and many residents ran out of their homes as quickly as they could.

Ma Liya, a resident in the county seat, told Xinhua that the streets were like a "battlefield after bombardment". She added that her neighbor's new two-story house was toppled.

"It's so terrible. The aftermath is much, much worse than what happened after the quake two years ago. I have never felt such strong tremors."

Ludian has a population of 265,900 in its seven townships.

Zhaotong city is on the earthquake belt and has been occasionally jolted by quakes.

In September 2012, a magnitude-5.7 earthquake caused more than 80 deaths and injured more than 800 people.

In 1974, a magnitude-7.1 earthquake in the same place caused over 1,400 deaths.

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Shan Juan, Wang Qian contributed to this story