Northern Territory authorities say it’s too early to know if a COVID-19 infected US man who travelled from Sydney to the Top End has infected others.

Contact tracers have identified 99 close and 304 casual contacts after the man in his 30s flew via Canberra to Darwin on Thursday for work.

No new cases were diagnosed overnight but many test results are pending as health workers race to contact the growing list of people potentially exposed.

More than a dozen close contacts are yet to be found and 11 have travelled interstate. Greater Darwin and Katherine remain locked down.

“We are not out of the woods but so far so good,” Chief Minister Michael Gunner said on Tuesday.

“We are not going to have a better picture until late tonight at the earliest.”

• See all of the NT’s exposure sites here

The man arrived at Darwin Airport on a Qantas flight just before midnight on Thursday and travelled to the Hilton Hotel by taxi.

He spent three days in the city before travelling on Sunday to Katherine, where he met a friend and visited Woolworths.

The man returned a positive COVID-19 result on Sunday after mandatory testing at Royal Darwin Hospital three days after arriving in the NT.

He’d earlier returned a negative test on August 10 during his stay in the Sydney quarantine hotel.

The man has been moved to the National Centre for Resilience quarantine facility where re-testing showed he had become more infectious than he was on Sunday.

“That means we detected the infection early. It also means he was more infectious in Katherine than he was in Darwin,” Mr Gunner said.

The friend in Katherine has returned a negative COVID result and has also been moved to Howard Springs.

There were 32 people on the man’s flight to Darwin. Six have since travelled interstate and authorities are attempting to contact them.

The other 25 are isolating in the NT, along with 11 close contacts from the Hilton Hotel.

The taxi driver and an Uber driver, who took the man to collect a hire car on Friday, are also considered close contacts but have returned negative tests.

NT Health is attempting to contact the Uber driver’s customers.

Numerous other exposure sites have been listed, including Outback Steaks and Curry in Darwin and Knotts Crossing Resort in Katherine.

Three people who were at the steak house when the infected man was present have since travelled to WA.

Another 12 are isolating in Darwin, along with 18 other people from Salvatore’s Cafe, a mini-mart, the hospital and Woolworths.

More than a dozen people who were potentially exposed to the virus at the resort have been identified, with 11 isolating and two interstate.

“We are now in a waiting game … We just need to wait and see what the outstanding test results come back as,” Mr Gunner said.

Authorities don’t yet know how the man contracted COVID-19 but they are treating it as the Delta variant.

About 150,000 people in Greater Darwin and Katherine were plunged into a three-day lockdown at midday on Monday.

Residents were given 90 minutes’ notice of the three-day lockdown, which is scheduled to end Thursday.

-AAP