China's Shenzhou VI has entered its second day in orbit, making it the country's longest manned space flight so far.
Astronauts Nie Haisheng, celebrating a birthday on Thursday, and Fei Junlong, carried out experiments on the craft's stability, state media said.
Experts were satisfied with the first day's progress, Xinhua agency said.
By noon on Thursday Shenzhou VI had circled Earth 18 times, with one orbit taking about 90 minutes.
It was an unusual 41st birthday for Mr Nie, whose daughter sang Happy Birthday to him late on Wednesday.
"It's marvellous around here. The Earth looks beautiful," Mr Nie told 11-year-old Tianxiang.
His wife, Wang Jie, said: "May you carry out the task entrusted to you by the motherland and return smoothly." Xinhua said that "at these words, Nie Haisheng was in tears".
The two astronauts were to spend Thursday taking on and off their space suits and opening and closing the capsule doors.
"They would purposely use more strength to move, so as to test the disturbance of people's movement on the spacecraft," according to Xinhua.
CHINA'S SPACE PROGRAMME
1958: Base for space flights built at Jiuquan, in Gobi desert
April 1970: First satellite launched
Oct 2003: First manned space mission on Shenzhou V
Oct 2005: Shenzhou VI takes two men into space
But Shenzhou VI, has deviated "slightly" from its preset orbit, moving a little closer to Earth than it is supposed to, according to Chinese state media.
As a result, the spacecraft will undergo its first orbit maintenance operation in the early hours of Friday to restore the vessel to its original trajectory.
The US on Wednesday congratulated China on a successful launch.
"We would applaud China and its success as only the third country to launch people into space," said Deputy State Department spokesman Adam Ereli.
Nasa also said it reaffirmed China's place, along with the US and Russia, in the space "elite".
"China, once again, has demonstrated that it is among the elite number of countries capable of human space flight," Nasa administrator Michael Griffin said in a statement.
The mission is expected to see the Shenzhou VI orbit the Earth for up to five days, during which the astronauts will carry out experiments.
Fei Junlong, 40 (left), and Nie Haisheng, 41
Both married with one child
Formerly in the air force - have more than 3,200 hours flying time between them
Joined space training programme in '98
Dining on Chinese specialities in space but chopsticks too difficult to use
It comes almost exactly two years after China's first manned space flight.
China's official media has speculated that the space capsule will circle the Earth up to 80 times before landing in the Chinese region of Inner Mongolia.
Beijing has attached great importance to its space programme, viewing it as a source of national pride and international prestige.
China hopes to set up a space station within five years and eventually it wants to put an astronaut on the moon.
CHINA'S SHENZHOU SPACECRAFT
1. Forward orbital module - crew live and work in this section, which contains scientific equipment. In future missions, this module may remain in space as part of a Chinese space station
2. Re-entry capsule - contains seats for three crew
3. Propulsion module - contains spacecraft's power unit and liquid fuel rocket system
4. Solar panels - spacecraft carries two sets with a total area of 40 square metres, which generate an average 1.5kW of power