After a textbook launch, Chinese space scientists on Wednesday undertook several experiments and a crucial manoeuvre to prepare for their first manned spacecraft's scheduled return to Earth on Thursday.

Shenzhou-5 is placed on a circular orbit 343 kilometres above the Earth, the official Xinhua news agency quoted a report by astronaut Lieutenant Colonel Yang Liwei and the Beijing aerospace command and control centre.

Yang spoke to his family and boss, Chinese Defence Minister General Cao Gangchuan, during which he said "hello" to people all over the world.

"I am feeling very good in space and it looks extremely splendid around here," he told his wife from outer space. He told his son that the sight of Earth from outer space was very "beautiful" and that he had recorded all that he had seen.

The spacecraft, powered by a Long March 2F carrier rocket, had a perfect lift-off at 9 am (6:30 am IST) from the Jiuquan satellite launch station in the Gobi desert in Gansu province.

After some manoeuvres, the spacecraft shifted from an elliptic orbit with a perigee of 200km and an apogee of 350km to a circular orbit 343km above the earth. The orbit shift was crucial to ensuring a safe landing for the craft, a top scientist said.

It is expected to orbit Earth 14 times before landing in the grasslands of Inner Mongolia province in northern China around 7 am (4:30 am IST) on Thursday.

The Shenzhou is based on the three-seat Russian Soyuz capsule, though with extensive modifications.

Analysts said by launching the multibillion dollar manned space mission, the Chinese government hopes to shore up national pride and demonstrate China's growing technological prowess.