A Chinese astronaut orbiting more than 300 kilometres (186 miles) above the Earth's surface delivered a video class to children across the country on Thursday, state television showed in a live broadcast.

Wearing a blue space suit, Wang Yaping, the second Chinese woman in space, demonstrated how a variety of objects -- from a bubble of water to a spinning toy -- behave in zero gravity.

Wang's class -- delivered from China's orbiting space module Tiangong-1 -- was shown in classrooms across China, state broadcaster CCTV said.

The astronaut smiled as she pushed a fellow astronaut into the wall of the module with the merest touch of her finger, and went on to gulp down a drop of water as it floated in mid air.

Using a live video link, Wang fired questions at students who gathered at a school in Beijing to watch the lesson on a giant screen.

More than 60 million students and teachers were expected to watch the class, the state-run China Daily said.

"In space... how can we tell if we have become thinner or fatter?" she asked students, with a red Chinese flag visible behind her.

"We can use electric scales," one eager young boy replied, dressed in a white shirt and the red scarf of the young pioneers, a youth organisation run by China's ruling Communist Party.

"I really envy you for being able to teach us a lesson while floating in space," a female student said.

"Have you seen any space junk?" another student asked Wang, before she replied: "We haven't seen any, but it does exist."

The lesson covered topics in physics including Isaac Newton's second law of motion, and the surface tension of water.

China launched three astronauts into space on board the Shenzhou-10 craft last week. The craft later docked with the Tiangong-1 in a test intended to prepare China to build its own permanent space station.

The astronauts on board went to space with specially prepared bags of lemon tea, and work out on exercise bikes, a video shown before the lesson revealed.

China first sent a human into space only in 2003 and its capabilities still lag behind the US and Russia. But its programme is highly ambitious and includes plans to build a station orbiting Earth by 2020, and land a man on the moon.

Beijing sees its multi-billion-dollar space programme as a symbol of its rising global stature, growing technical expertise, and the Communist Party's success in turning around the fortunes of the once poverty-stricken nation.

The project is heavily promoted to the domestic audience, and state broadcaster CCTV ran the lesson in full on its premier channel.