Pang Jiaying, Liu Jing, Zhu Qianwei and Yang Yu (L to R) pose for photos at poduim in Rome, Italy, July 30, 2009. China snatched the women's 4x200m freestyle relay gold medal in a world record time of seven minutes 42.08 seconds at the world swimming championships Thursday. [Xinhua]

Chinese swimmers swept two titles out of five at stake on Thursday to raise their swimming gold tally to three at the world championships in Rome.

Zhao Jing shattered the women's 50m backstroke world record with a time of 27.06 seconds to win the world title.

"It's my first world championship and this gold was beyond my wildest dreams," said Zhao, who bettered the previous mark of 27.38 seconds set by Anastasia Zueva in the semifinals.

Germany's Daniela Samulski claimed silver in 27.23 seconds and China's Gao Chang placed third in 27.28.

China rounded off the night by shattering the world record to take gold in the women's 4x200m freestyle relay.

The team of Yang Yu, Zhu Qian Wei, Liu Jing and Pang Jiaying timed seven minutes 42.08 seconds, more than two seconds faster than Australia's mark of 7:44.31 set at the Beijing Olympics.

Defending world champions the United States picked silver with Britain taking bronze.

Earlier, American Ryan Lochte clocked a world record of 1:54.10 to win the men's 200m individual medley gold and Brazil's Cesar Cielo Filho triumphed in the men's 100m freestyle final in 46.91, also a world record.

Australian Jessicah Schipper won the women's 200m butterfly in a world record of 2:03.41.

Schipper's compatriot Christian Sprenger set the men's 200m breaststroke world record in the semifinals with a clocking of 2:07.31.

In the women's 200m breaststroke semifinals, Canada's Annamay Pierse posted a world mark of 2:20.12.