By Lloyd Jones in Darwin

Residents of an already-saturated Top End town are cautiously optimistic they will avoid a second wave of devastating flooding after an ex-cyclone swept past.

Homes and businesses in the town of Katherine were inundated earlier in March after heavy rains filled catchments in the Northern Territory’s big rivers region.

Major flood warnings have been issued again for Katherine and other communities across the NT’s north as ex-tropical cyclone Narelle – now classified as a tropical low – heads into Western Australia.

Katherine mayor Joanna Holden said her community was not out of the woods yet, but it was better prepared this time around after a major sandbagging effort.

There hadn’t been heavy rainfalls overnight and the falls up in the river catchment area had mostly been under 100mm, she told AAP on Monday.

“So I think people are feeling mildly optimistic, but obviously with all that’s gone on you just don’t know.

“There is a major flood warning in place. We can’t become complacent. Just because we didn’t have 200mm fall last night doesn’t mean we’re out of the woods just yet.”

Residents are watching the water level gauge on the town bridge as an indicator of whether roads would be closed and homes inundated again, she said.

An emergency field hospital has been set up in Katherine by the National Critical Care and Trauma Response Centre, the first time such a mobile facility has been activated in Australia.

Katherine Hospital has been closed due to the flood risk and the field hospital will provide emergency and primary care, as well as maternity and radiology services.

The major flood level had been reached at Adelaide River, south of Darwin, impacting a few homes and causing power cuts and a boil-water alert, NT Chief Minister Lia Finocchiaro said.

The Daly River township, northwest of Katherine, remains underwater with more flooding expected as hundreds of evacuated residents wait in emergency shelters in Batchelor, south of Darwin.

Narelle weakened to below cyclone strength after crossing the coast in remote eastern Arnhem Land on Sunday, with trees down but no reports of major damage in Gulf of Carpentaria communities.

Hundreds of residents from the gulf community of Numbulwar were flown by the RAAF to Darwin ahead of the storm and hope to return home soon.

The ex-cyclone is forecast to continue its path into WA on Monday, bringing heavy rain and damaging wind gusts to northern parts of the Kimberley.

Catchments were already saturated across the region, meaning rivers and creeks would rise quickly with heavy rainfall, the Bureau of Meteorology said.

Roads may be affected and some communities may become isolated, it warned.

There was a high chance of the system redeveloping into a tropical cyclone by early Wednesday to the north of the Pilbara coast as it moved west.

Meanwhile, the clean-up continues in far-north Queensland after Narelle struck on Friday.

State schools have reopened and power is being restored across the remote region after the cyclone uprooted trees and blew off roofs.

Fuel has also been delivered by police to Cape York communities to help locals recover from the storm.