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 on April 8, 2006.

About 200 people are said to have seen either a flying saucer or crop circles near Westall High School on April 6, 1966. The craft was described as silver, saucer-shaped and silent.

Some witnesses 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.

Canberra academic Shane Ryan says he has contacted about 50 witnesses in the past year. The bulk were Westall High School students who were gathered on the oval at the time for physical education.

The incident was reported in daily papers, on Channel 9, and twice as front-page news in the local Dandenong Journal.

About a quarter of the witnesses said they saw the flying saucer and the rest saw as many as five 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 that ... after the incident, "guys in uniforms" made the resereve a no-go zone. Mr. Ryan said many witnesses reported police or military activity after the incident.

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.