China's ambitious space programme is set to take a giant leap forward this week when three astronauts blast off on a mission to undertake the country's first space walk.

The Long March rocket, taller than the Statue of Liberty, is already in position at the northwestern Jiuquan launch centre to lift the Shenzhou VII capsule into orbit for China's third manned space flight late on Thursday.

According to government websites, Air Force Colonel Zhai Zhigang, 42, will make history as China's first man to walk in space when he steps out of the Shenzhou capsule either Friday or Saturday.

The 68-hour mission will bring China closer to its goal of building a small space laboratory -- and later a space station -- and further ramp up national pride after the Beijing Olympics and ahead of National Day on October 1.

"My impression is that everything is going well in the final days before the launch," said Morris Jones, an Australian space analyst and writer for SpaceDaily.com who has closely studied China's space efforts.

"I don't think there are any major problems. They have had a long time to get ready for this," he told AFP.

China became the third nation after the United States and Russia to independently put a man in space when Yang Liwei, a fighter pilot, flew aboard the Shenzhou V in October 2003.

In 2005, two astronauts or "taikonauts" manned the five-day Shenzhou VI mission as the nation announced vague goals to eventually build a manned space station and put a man on the moon.

"The Chinese programme overall can be described as ambitious, yet incremental and prudent," Joan Johnson-Freese, an expert on China's space effort at the US Naval War College, told AFP.

"The consistent increase in the number of astronauts flown is consistent with that approach, and consistent with the model used earlier by the Soviets and Americans."

Perfecting space walk technology will be crucial for China's plans eventually to build a space laboratory and space station, Johnson-Freese said.

Zhai will also test the reliability of China's first space suit as he manoeuvres around the craft and releases a small satellite to broadcast video images of his walk.

"This flight is part of the approved, official Chinese manned space plan for proven manned space-flight capabilities," Johnson-Freese said.

"Shenzhou VII puts them one step closer to (building a) small space lab."

Riding with Zhai in the spacecraft will be Liu Boming and Jing Haipeng, both also 42 and air force fighter pilots. All three were selected in 1998 as part of a team of first-generation taikonauts.

The Shenzhou -- which means "Divine Vessel" -- is made up of a service module that powers the craft, a return module and an orbital module that has the capability to stay in space after the taikonauts return to earth.

According to Qi Faren, a retired top engineer in China's manned space programme, the next Shenzhou mission will come in 2010 when China will attempt to build a space laboratory.

Three missions will fly in succession with the first two flights unmanned and slated to place two orbital modules into outer space as the building blocks for the laboratory, Qi told the Oriental Daily.

The manned Shenzhou X flight will then dock with the two orbital modules and begin a series of scientific experiments, he said, adding that China hopes to build a space station in 2020.

The latest mission will be closely watched by the United States, among others, after China shot down one of its own satellites last year in a move that raised international concerns over its military ambitions in space.