SYDNEY (AFP) - Power was restored to Darwin on Wednesday after a 12-hour outage across the northern Australian city caused chaos, with schools and public sector offices closed and traffic lights knocked out.

A tripped circuit blacked out the city of some 120,000 people and towns up to 320 kilometres away, with the government mobilising emergency management protocols as technicians desperately worked to fix the problem.

"Power and Water apologises to customers for today's extended outage," the electricity provider tweeted several hours into the emergency.

The Northern Territory government said all schools were closed for the day, and the public bus network suspended.

"Unless advised by their department, Territory public servants are encouraged to stay at home and await further advice on power restoration," it added.

The local hospital and airport operated as usual, although some hotels were evacuated as customers sweltered through the night with air conditioners out of action in the steamy, tropical city.

Water and sewage services were supported via generators.

At the height of the crisis, Deputy Chief Minister Dave Tollner urged calm.

"People need to stay calm ... and be careful on the roads as traffic lights are down across the city," he was quoted as saying by the Northern Territory News.

The newspaper said the city "eerily resembled a ghost town".