A Chinese rocket with three astronauts on board blasted off this afternoon on a mission which will see the first Chinese making a space walk.

The launch of the Shenzhou VII is China's third manned space venture since October 2003, when it joined Russia and the United States as the only countries to have sent astronauts into space. The space walk is expected on Saturday.

China sent two astronauts on a five-day flight on its Shenzhou VI craft in October 2005.

President Hu Jintao stood before the three white-suited astronauts before they headed toward the Long March rocket.

"This will be a major step forward for our country's aerospace technology," he told them at the Jiuquan launchsite in barren northwest Gansu province.

"You can certainly fulfil this glorious and sacred task. The motherland and its people await your triumphant return."

Officials and state media have hailed the prospective space feats as national triumphs, crowning the successes of the Beijing Olympics and dramatising the country's broader ambitions.

"This will be a very outward show of Chinese power," said Kevin Pollpeter, an expert on China's space programme at the Defense Group Inc in Washington.

"The eventual goal is to build a space station. For them, that's become one of the trappings of being a great power."