The damage wrought by Tropical Cyclone Marcus is a "real wake-up call" for Darwin residents lulled into a false sense of security when it comes to cyclone safety, emergency services say.

Key points: Tropical Cyclone Marcus has left fallen trees and power lines across Darwin

Tropical Cyclone Marcus has left fallen trees and power lines across Darwin Residents have been urged to stay indoors and off the roads, as hazardous power lines litter the city

Residents have been urged to stay indoors and off the roads, as hazardous power lines litter the city People are also advised to boil water, as the extent of contamination is unknown

The category two storm passed over the city just before midday on Saturday, and was downgraded to a category one system about 4:00pm CST.

Darwin saw persistent gale-strength winds of over 62 kilometres per hour for six hours, and recorded a maximum wind gust of 130 kilometres per hour while Marcus was passing overhead.

Authorities said the direct threat of impact from the cyclone had ceased for the city, and conditions were expected to ease overnight.

But NT Police regional controller Warren Jackson said the amount of damage visible across the city from the category two system was a warning of what stronger cyclones could do.

"This is a real wake-up call for Darwin, given that was in what we'd say was the lower end — but it was a category two — you can see there was a significant amount of damage with trees fallen, houses have been damaged … a significant amount of rain has fallen in a short period of time which flooded roads … but as a result of that people still didn't heed our warnings."

A number of people took unnecessary risks during the height of the storm, he said.

"We watched people put themselves in peril today, despite all the warnings in the middle of the storm we saw people driving around into flooded waters, around fallen trees," he said.

"We saw people in the event itself outside of shelters — all they're doing is putting themselves in danger. If they were expecting Emergency Services to come and assist them, that wasn't necessarily going to be the case.

"If you don't necessarily need to travel then reconsider what the purpose of leaving your house or other accommodation is."

Sorry, this video has expired Cyclone Marcus brings down power lines

Emergency situation still in place

Motorists have been urged to stay off the roads, as power lines have been knocked down throughout the city, and another large weather band is approaching that could bring more wind and heavy rain.

NT Emergency Services was working through a call log of around 400 incidents across the region as of Saturday evening, spokesman Jason Collins said.

Most of those were to do with fallen trees, he said, but up to 25,000 homes were without power which would take at least a day to rectify.

"An emergency situation is still in place, the weather may be clearing but it's still not safe outside," he said.

"We still ask people to be alert, be aware, the conditions are still not safe, I can't say that enough.

"We have trees down, we have power lines down, those power lines can still be live and will be live into this evening."

A resident surveys the damage caused by Cyclone Marcus to his street in Coconut Grove. ( ABC News: Neda Vanovac )

He urged residents to stay away from floodwaters, beaches, and waterways.

Hundreds of emergency services personnel would be moving around over the next few days clearing debris and restoring power and water, he said, with the hospital, airport and power and water sites being the priority.

Defence personnel will be helping clear the streets on Sunday.

"We can safely say it will be well into Sunday before we've got a lot of the trees cleared and the power lines made safe, so we need people to really be thinking about what they're doing and do you really need to be going out? If it's not essential, don't go," Mr Collins said.

Survey teams were only a few hours into their work and it was too early to estimate what the damage bill would be, he said.

Sorry, this video has expired Man almost hit by tree during cyclone

Two rescues, reports of looting

There were only two main incidents on Saturday and so far no other rescues, Mr Jackson said.

Two people were rescued after a boat broke from its moorings and crashed into their vessel at the Dinah Beach boat ramp.

The NT water police entered the water on jetskis as there were concerns one boat was taking on water. One of the two people on the boat was in their 60s and had a respiratory problem.

At Coolalinga, a tree fell onto a gas cylinder at a petrol station, sparking an evacuation of the surrounding area.

There were reports on social media that the Karama post office and a local car dealership had been broken into.

Mr Jackson said police had not yet had reports of looting, but that it was a concern.

"Crime is always a concern in an emergency situation because people do take advantage of those that are vulnerable … away from their businesses, their houses, whatever the case may be, and it's unfortunate," he said.

Sorry, this video has expired Two rescued by water police during cyclone

Water boil alert following contamination

It will also be another day or two of drinking bottled water or boiling water after the Department of Health issued a boil water alert for all residents due to damaged infrastructure.

It is anticipated that a boil alert will remain in place for at least 48 hours.

"We would advise people to boil the water and allow it to cool prior to consumption or for use for oral hygiene purposes," Public Health director Xavier Schobben said.

"The alert will be lifted following government laboratory results indicating the water supply is bacteria-free."

An evacuation has been ordered around a service station in Coolalinga after a tree hit a gas cylinder. ( Facebook: Danielle Fisher )

He said the major focus now was on water quality, food safety, and taking care while cleaning up.

Residents without power were urged to eat perishables from their fridges first, followed by frozen food, and then tinned and dry goods.

Those without running water should drink water from their cyclone kits or ask family and friends to help, Mr Schobben said.

"If you don't know your neighbours, now's a good time to get to know them. Everybody, help out," he said.

A blown-over stage and broken trees at Darwin's Ski Club. ( Facebook: Elizabeth Bonnie )

Cyclone heads for the Kimberley

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On Saturday afternoon, gales with gusts to 110 kilometres per hour were being felt along the coast between Cape Hotham and Dundee Beach and southern parts of the Tiwi Islands.

The gusts could extend further south to Wadeye by early Sunday morning.

They will be higher than normal between Wadeye and Cape Hotham, and along the south coast of the Tiwi Islands.

Destructive winds with gusts greater than 150 kilometres per hour may develop over the Kimberley coast later on Sunday, affecting the WA towns of Kununurra and Wyndham.

Large waves may produce minor flooding of low-lying coastal areas on Saturday night.

Residents from Cockatoo Island to Mitchell Plateau should remain on alert.

Cyclone Marcus is forecast to re-intensify to a category two system before approaching the northeast Kimberley during Sunday.

Numerous houses throughout Darwin had tree damage after the cyclone. ( ABC News: Neda Vanovac )

Services, events suspended

All flights to and from Darwin were cancelled on Saturday, public transport was not operating, and Casuarina Square closed for trading.

The Northern Territory Electoral Commission postponzed the Palmerston Council election for a week, and the Tiwi Islands Football grand final has also been postponed until March 25.

AFL NT confirmed Saturday's grand final set would be postponed to a later date.

Even though the Parap markets were cancelled (as were the Sunday Nightcliff markets), one man came along to sell flowers anyway.

He said he wasn't going to let Tropical Cyclone Marcus force him to miss the markets for the first time in 38 years.

"I have a lot of regular customers and I have a lot of orders to deliver today. So I can't just abandon those people," he said.