Astronauts Fei Junlong, 40, and Nie Haisheng, 41, both colonels in the People's Liberation Army, were handpicked from 14 fighter pilots and had been in the running for China's first
manned space launch in 2003.
"There is nothing to worry about," state television quoted the pair as saying before Shenzhou VI lifted off as a light snow fell.
"We will accomplish the mission resolutely. See you in Beijing."
"I feel good," Fei, a native of Kunshan, said minutes after the blast-off from the Jiuquan Satellite Launch Centre, deep in the desert of the northwestern province of Gansu.
State television broadcast the lift-off live and showed the pair inside the Shenzhou capsule waving at the camera after the spacecraft entered orbit.
The capsule, based on the Russian Soyuz spacecraft developed in the late 1960s and is still in service, is due to touch down in the remote northern region of Inner Mongolia on Monday.
Fei Junlong (L) and Nie Haisheng
vowed to accomplish their mission
An elated Premier Wen Jiabao and other leaders were in Jiuquan to witness the launch.
"You will once again show that the Chinese people have the will, confidence and capability to mount scientific peaks ceaselessly," the official Xinhua news agency quoted Wen as telling the astronauts.
China had stressed on Tuesday that its space programme was
peaceful and it did not want to enter any arms race in space.
In the Chinese capital, President Hu Jintao and Vice-President Zeng Qinghong watched the liftoff at the Beijing Aerospace Command and Control Centre.
China is determined to become a serious space player and set up a National Astronaut Training Centre in Beijing this week.
Mooncakes and congee
Xinhua said it was only the third such facility in the world.
"We should never slacken our efforts to explore the mystery of space," Nie, described by Xinhua as a "cowboy", said.
President Hu Jintao congratulates
the rocket launch team
Once in orbit, promptly helped themselves to pineapple-filled mooncakes - traditional heavy pastries - for breakfast, state television said.
The spacecraft has been packed with a wide range of rations, from green vegetables and braised bamboo shoots to rice and bean congee (a type of rice porridge), that can be easily rehydrated and then heated in a machine that looks like a toaster.
China's first man in space was Colonel Yang Liwei, who orbited Earth 14 times on board Shenzhou V craft in October 2003.
The former Soviet Union and the US put their first men into space in 1961.
China has had a long - if not always successful - relationship with space travel.
The astronauts ate traditional
mooncakes inside the capsule
The country invented gunpowder and legend has it that a Ming dynasty (1368-1644) official named Wan Hu attempted the world's first space launch.
He strapped himself to a chair with kites in each hand as 47 servants lit 47 gunpowder-packed bamboo tubes tied to the seat.
When the smoke had cleared, Wan was apparently found to have been obliterated.
But the dream survived and has become reality.