The quake hit mid-morning and was centered about 500 kilometers (300 miles) north of Darwin, the capital of Australia's Northern Territory, Geoscience Australia seismologist Cvetan Sinadinovski said.

"The earthquake would have been felt by almost everyone indoors," Sinadinovski said.

"The earthquake occurred 500 kilometers from Darwin, in a region known for its moderate seismicity," he said of the temblor caused by a collision between the Australian and Asian tectonic plates under the Banda Sea.

"People would have felt this earthquake up to 500 kilometers away from the epicentre, and we have heard numerous reports of residents in the Darwin area having felt the effects of the event," he said.

Among those shaken by the quake were the judge, jury and others involved in the Darwin trial of Bradley John Murdoch, a mechanic charged with the 2001 disappearance and presumed murder of British tourist Peter Falconio, the national news agency AAP reported.

Chairs and TVs in the court building shook and the judge in the case, Chief Justice Brian Martin, remarked: "I think we just had a minor tremor."

The Bureau of Meteorology's Darwin office said no reports of damage have been received by police.

The biggest earthquake to strike northern Australia hit in 1998 with a magnitude of 6.9, Sinadinovski said.

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