FIVE mine workers are convinced they saw a UFO fly over them on a remote Territory island.

Mine maintenance worker Arnold Murray said a bright object whizzed over the Gemco mine site on Groote Eylandt as he and his colleagues started the night shift last Friday.

Mr Murray, 32, said the bright light was slightly higher than a plane coming to land -- but it was silent.

He and four workmates were at the mine site at 7.15pm when he saw an object flying towards them.

''I noticed a star in the sky and it was getting closer,'' he said.

''As it approached I realised it was at plane level.

''Four other lads walked out of the office and we watched it for a little while. It was vertical from us, there were no flashing lights or noise.

''The plant's pretty quiet at night. (It made) no noise whatsoever.

''All of a sudden it shot off and left a long orange trail behind it. That orange trail just faded out like a shooting star.''

Mr Murray said they wanted to know what flew over their heads in the night: ''It wasn't a chopper, it wasn't a plane, we knew that much, and it definitely wasn't a shooting star.''

''It blew us out of the water.''

Defence spokeswoman Kelly Cooper said the object was not a military plane: ''There were no military aircraft flying in that area at that time on that day,'' she said.

She said any navy ships letting off flares would have been at least 200 nautical miles off shore.

Groote Eylandt, in the Gulf of Carpentaria, is near one of the first and most famous UFO sightings in Australia -- the ''light wheel'' reported on January 23, 1964.

Sailors on a vessel off the northeast point of the island reported seeing a circle of pulsing lights rotating clockwise, and they said their compass went ''haywire''.