DARWIN has been rocked by an earthquake measuring 6.8 on the Richter scale, Geoscience Australia said last night.
The government agency which measures earthquakes said the quake struck at 8.21pm (CST) or 9.51pm (AEDT) last night.
Its epicentre was in the Banda Sea near Indonesia.
There were no immediate reports of damage but the quake was felt across the city and at least 140km from Darwin, Geoscience Australia spokesman Chris Thompson said.
"We've got a preliminary report of an earthquake ... of magnitude 7.5," he said.
"They are preliminary figures and we will be confirming that shortly."
Darwin resident Paul Dyer, who lives about 3km from the CBD, had just sat down on his couch at home when the earth began to shake.
"I'm in a ground-level house and the house was shaking like there's no tomorrow," he told AAP.
"I was sitting on the couch and could feel the ground shaking.
"It was pretty full-on, there's bound to be some structural damage somewhere."
Dr Mark Leonard from Geoscience Australia said subsequent readings measured the earthquake at magnitude 6.8.
He said the quake struck in the Banda Sea 800km north of Darwin at latitude 6.5 degrees south, 129 degrees east.
Although it was the biggest in several years in the Banda Sea, the quake was unlikely to have done any significant damage and "very unlikely to cause a tsunami", Dr Leonard said.
"The Banda Sea is one of the most seismically active areas in the world and gets an earthquake of about magnitude 5 every couple of months," he said.
A Northern Territory police spokeswoman said there were no reports of damage and Darwin was carrying on as normal.
"There's absolutely nothing," she said.
"I've had no reports of injuries, no reports of evacuations, no reports of damage."
Resident Mike Emerson was in Newcastle at the time of the December 1989 quake which measured 5.6 on the Richter scale and killed 13 people.
He said last night's quake felt comparatively minor.
"It only lasted a few seconds. A few little waves went through the concrete floor, and the fans rocked back and forth. But there was no damage (here)," Mr Emerson said.
ABC reporter Lindy Kerin, who was at work at the time, said: "It was a bizarre feeling. I had a glass of water on my desk (at work) and it was wobbling."
Ms Kerin said some of her colleagues sheltered under door frames, considered the sturdiest part of a structure in the event of an earthquake or cyclone.
A receptionist from the Mirambeena Resort in Darwin said: "There were three separate tremors, two little ones and then a big one" but there was no damage.
"We're on the ground floor and it shook a fair bit for a couple of minutes," she said, adding that "everyone is going about their business".
The hotel, based near the city's centre, was almost full, with 215 rooms booked, but everyone stayed in their rooms, she said.
Darwin's SkyCity Casino and hotel said no one was evacuated from the beachfront building, despite earlier media reports.
A security surveillance worker said some patrons stepped outside the three-storey building of their own accord but returned soon afterwards.
"Every guest in the venue felt it, the phones were going hot for a while ... everyone's having a laugh about it now."
He said once staff were told the quake occurred in the sea they pointed a camera on the beach "just in case".
Northern Territory News journalist Barry Doyle said he had been told the quake occurred 660km north of Darwin in the Banda Sea but tremors were felt as far south as Katherine.
"We had two good shakes. Probably the best shakes we've had," Mr Doyle said.
"It moved the building we're in and it's certainly got the town talking but there's no truth to the rumour that it was caused by Prince Charles putting $200 on the bar in Alice Springs."
A Royal Darwin Hospital spokeswoman said the hospital had not received any patients with injuries from the tremors and no equipment had been affected at the hospital.
A Power and Water spokesman said the power supply company had not received a single call for help and there were no known blackouts or damage to powerlines.
