Royal Australian Navy personnel work with civilian emergency services to evacuate members of the public in Cairns, Australia, Dec18, 2023. (AISTRALIAN DEFENSE DEPT VIA AP)

CANBERRA - Evacuations have been ordered from a remote region of Australia's Northern Territory amid warnings of a "one-in-a-hundred-year" flood.

Authorities in the NT on Wednesday night began evacuating hundreds of residents from the town of Borroloola, more than 700 km southeast of Darwin, and its surrounding areas with the assistance of the Australian Defense Force.

The evacuations were ordered by the NT government after updated modeling predicted water levels in the McArthur River could rise to 18 meters at Borroloola following heavy rainfall brought by ex-tropical cyclone Megan.

A peak of 18 meters would be the highest water level in recorded history for the river, surpassing the 15 meters that caused significant flooding in 2001.

Initial plans for the ADF to evacuate approximately 700 residents from Borroloola were suspended on Monday due to deteriorating weather conditions preventing aircraft from landing safely in the area

NT Police Commissioner Michael Murphy said at a press conference that previous modeling had underestimated the impact of the rainfall, predicting a 15.3 meter peak.

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He said any peak exceeding 14.9 meters would represent a major flooding event.

"A one-in-a-hundred-year flood is really serious," Murphy told reporters.

"We're taking it incredibly seriously and we're doing everything we can to ensure the residents of Borroloola are safe."

Initial plans for the ADF to evacuate approximately 700 residents from Borroloola were suspended on Monday due to deteriorating weather conditions preventing aircraft from landing safely in the area.

Ex-tropical cyclone Megan made landfall on the NT mainland on Monday afternoon 50 km from Borroloola as a category 3 storm, bringing with it heavy rainfall and wind speeds of up to 200 km per hour, after causing widespread damage on islands off the northeast coast over the weekend.

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It caused minimal damage to buildings and infrastructure on the mainland before being downgraded to a tropical low storm on Tuesday.

As of Thursday morning, the storm was approaching the NT's border with Western Australia (WA), where it was continuing to bring heavy rainfall and strong winds, prompting severe weather and flash flooding warnings from the Bureau of Meteorology.