ONE of Australia's biggest UFO mysteries has taken off again, 40 years on.

And researchers hope the truth will out at a reunion of more than 30 witnesses tomorrow.

About 200 people are said to have seen either a flying saucer or crop circles near Westall High School on April 6, 1966.

Witnesses described the as silver, saucer-shaped and silent. Others who saw the object say they saw it drop behind trees at Westall's Grange Reserve, then rise vertically and leave.

Flattened and charred grass "crop circles" were said to have been left behind in the reserve.

Canberra academic Shane Ryan, who has formed an online contact group for witnesses, says he has contacted about 50 witnesses in the past year.

Most of those who witnessed the event were Westall High School students who were gathered on the oval at the time for physical education classes.

The incident was reported in daily papers, on Channel Nine and ran for two weeks as front-page news in the Dandenong Journal.

About a quarter of the witnesses said they saw the flying saucer and the rest saw as many as five so-called crop circles.

Many children reportedly ran down to the Grange after the sighting.

John Spencer, a seven-year-old at Westall Primary School at the time, said the incident still got to him. "I need answers, 'cos this has been a real bugbear over the years," he said.

"I have remembered the day as vividly as a seven-year-old could, Mum dragging me away from the Grange after school from the landing site . . . seeing this object in the sky, other planes flying, following it."

Mr Spencer said the Grange was a second home to kids, a spot to catch frogs and tadpoles.

He said that after the incident, "guys in uniforms" made the reserve a no-go zone.

Mr Ryan said many witnesses reported police or military activity after the incident. Witnesses say that the uniformed men who appeared after the incident set fire to the paddock, destroying circle patterns seen on the grass after takign measurements.

Students and staff all reported being told not to talk about the incident. Students were even reportedly disciplined for speaking about the alleged sighting.

Westall Science teacher Andrew Greenwood told the Dandenong Journal at the time he saw a silvery-green disc.

Mr Greenwood also claimed he was visited at home by two uniformed officers and threatened with prosecution if he continued to speak of it.

The Defence department says there is no record of any military action after the sightings.

Gerry Shepherd taught woodwork at the time and says he never saw any military at the school.

"All I can say is that the school bell went to start the afternoon classes and there was hardly anyone there," Mr Shepherd said.

"I would say 99.999 per cent it's a load of bull."

Mr Ryan hopes retired police or military will go to the reunion, from 11am-2pm at Westall Tennis Club on the edge of the Grange in Clayton South.

"I'm convinced people saw something quite out of the ordinary," he said.

"It is a story that has almost been completely forgotten.

"These people, even after 40 years, have this burning desire to make sense of what they saw."

Visitors to the support group's website invites witnesses to tomorrow's reunion. "We are all rational people looking for answers to a 40 year old mystery," says a posting. "Maybe your piece of information will be the last bit of the jigsaw puzzle to lay this thing to rest."