China on Friday launched its Shenzhou VII manned space mission carrying three astronauts whose main task was to complete the country's first spacewalk.

The spacecraft lifted off from the Jiuquan space centre in the north-western province at 9:10 pm (1310 GMT) on board a Long March-2F carrier rocket.

The scheduled three-to-four-day Shenzhou VII mission includes China's first spacewalk on Friday, which is expected to last about 40 minutes and be carried out by astronaut Zhai Zhigang 343 kilometres above the earth.

President Hu Jintao and other leaders of China's ruling Communist Party travelled to Jiuquan to watch the launch, which was shown live by state broadcaster China Central Television.

All systems were normal for the first 15 minutes of the space flight, according to mission control staff heard speaking in the television broadcast.

Hu saw off the astronauts late Thursday at Jiuquan before they headed to the nearby launch-pad.

He praised the astronauts, who are all former military fighter pilots, for their "excellent quality," in a brief meeting some three and a half hours before the launch.

Flanked by civilian and military leaders of the space programme, Hu addressed the astronauts as "comrades" as they sat behind a protective glass screen in their space suits.

"I come here on behalf of the Communist Party, the State Council and the Central Military Commission, and the people of our whole nation, to encourage you in this mission, and I wish you every success," Hu said in his speech, which was broadcast live by state television.

"We believe you will certainly complete your mission and we hope you can return safely and successfully," he said.

The government said astronaut Zhai Zhigang was chosen to make Friday's spacewalk, which forms the key part of the three-day mission.

The other two crew members are Liu Boming, who will assist Zhai with leaving and re-entering the spacecraft, and Jing Haiping.

The three men, all 42, saluted Hu and the other leaders before leaving for the launch-pad, where the Shenzhou VII spacecraft and its Long March-2F carrier rocket were installed last weekend.

"Please let the whole nation rest assured, we will obey the orders and instructions, work carefully and try to keep ourselves calm to make sure we complete our mission," Zhai said at the send-off ceremony.

In 2003, China's successful Shenzhou V mission made it the third country to launch a manned space mission, after Russia and the United States.

Shenzhou VI carried two astronauts into space in 2005.

Shenzhou VII is the next stage of China's plan to build an integrated ground-space network for space exploration and manned space research, including a permanent space laboratory by 2020.