Essential Services Shadow Minister Joshua Burgoyne said the blackout, which affected Darwin, Palmerston and Katherine, was damaging to businesses and threatened people's health.

"Yesterday's blackout ... caused many businesses to close and heightened the health risks for vulnerable Territorians who struggled to stay cool during the hot and humid conditions without power," said Mr Burgoyne.

He said reliable power will come from a focus on renewable energy.

"The government needs to focus on both renewables development and providing stable and reliable power, with the wet season approaching," he said.

"I call on the government to renew its focus on ensuring quality power infrastructure across the Territory."

"Power is a basic essential service, critical for our society and our economy to operate smoothly and safely."

The blackout was blamed on a problem with the generators at the gas-fired Channel Island power station.

Mr Burgoyne said the Channel Island station is ageing and in need of government repair.

"While a gas supply issue is being blamed for the outage, we know the Territory's power infrastructure at Channel Island is ageing under a government which has shifted its focus away from ensuring a reliable and secure power source for the Territory," he said.

The first units at Channel Island, in Darwin Harbour, were commissioned in 1986.

The blackout was triggered just after 4pm, and a slow restoration process began after the fault had been repaired just after 6pm.

Power officials said the gas problem has been fixed.

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