It has also won official acknowledgement, having been recognised recently by the Government as a legal entity.

'The Government pays more attention to us because decision-makers are more interested in listening to scientists,' said Mr Chen, who has a doctorate from the Beijing Aviation and Space University.

Sightings of UFOs are recorded in ancient Chinese history. During the Jin Dynasty, in 315 AD, one scribe wrote that a 'sun' fell to the earth, and three others were seen flying towards the east.

During the Cultural Revolution, UFOs, like most everything else, were banned by China's xenophobic ideologues. But in the late 1970s, the political atmosphere cleared up and UFO enthusiasts took advantage.

Upon hearing of sightings, Mr Chen's group sends out questionnaires to the witnesses asking for all the details so the society can investigate.

For a taste of the detailed follow-up the society undertakes, Mr Chen, just back from Heilongjiang, recounts the story of Meng Zhaoguo, a worker at a tree farm in that province.

Mr Meng saw a large white mass land on a mountain and thought it was a weather balloon which he could sell to a factory to make shoes or gloves.

But when he and his friend got within 150 metres of the long, white object, it started to shriek. They approached the object from the other side of the mountain, but when they got close their skin began to feel numb and the object shrieked again. So the two ran back for reinforcements.

The Communist Party secretary and the manager of the tree farm wondered if it might be a secret weapon being developed by the Chinese military, or possibly a tool of Russian espionage. With 30 workers in tow, they all went back to the mountain.

This time, Mr Meng suddenly dropped to the ground and seemed to have lost touch with reality. The workers took him back to a shelter, where he did a handstand and knocked over the ramshackle structure. A doctor was called, but he could not get his stethoscope near Mr Meng's body.

'It was repelled by a force, just like when two negative sides of a magnet come together,' said Mr Chen. Mr Meng fell into a sort of coma.

On July 17, Mr Meng suddenly disappeared from his bed in the middle of the night. He turned up in the morning wearing only underpants. All the doors and windows of the house were locked, meaning he had not walked out of the house, Mr Meng's wife testified.

As it turned out, he had been whisked away by an extraterrestrial woman who took sexual advantage of the handsome worker - repeatedly.

The woman from Jupiter showed Mr Meng pictures of her home, which she escaped as Comet Shoemaker-Levy 9 hurtled towards her planet last July.

Mr Meng's case is still under investigation.

Peasants often think UFOs are gods or ghosts, while scientists tend to look at them as manifestations of natural phenomena.

The UFO Society, said Mr Chen, plays an important role because its hypotheses can combat superstitious interpretations of strange sightings and happenings without necessarily dismissing the extraordinary as tricks which nature plays on the human eye.

'From a philosophical point of view, there are lots of systems in the universe like our solar system. Many of them have conditions which can support life. We shouldn't think that earth is the centre of civilisation in the universe,' he said.

Over the past 10 years there have been 5,000 reports of UFOs in China.

Around national day this year, 26 cases were reported in Beijing alone. On October 4, at a town near the Great Wall, a man saw five spacecraft flying silently at high speed in a V-formation.

On October 6, four men living near the Drum Tower in the capital saw an oval-shaped object the size of a basketball with flashing lights floating horizontally for about five minutes. Then it suddenly took off, lights flashing.

Unlike UFO groups in other countries, China's UFO Society does not just try to track down cases, said Mr Chen, but is also involved in theoretical research.