The Northern Territory has reported 546 COVID infections as the government apologises for an embarrassing exposure site reporting failure, saying it has “no excuse”.

Friday’s new infections bring the territory’s total active caseload to about 3300 with 27 – three more than the previous day – in hospital.

Twenty patients are considered acute or suffering serious symptoms and one is in intensive care in Royal Darwin Hospital.

About 75 per cent of infections are in the Darwin region, including Palmerston and the rural areas,” Chief Minister Michael Gunner said.

Another 15 per cent are in Alice Springs, 5 per cent in Katherine, 320 kilometres south of Darwin, and 4 per cent in East Arnhem Land. The rest are in other regional areas.

Mr Gunner admitted the territory’s new COVID-19 exposure-site messaging system linked to the check-in app had not been operating as planned.

“Over the past week these messages have not been sent,” he said. “There is no excuse for this.”

Mr Gunner said instructions had been given to a government team to set up the new system by the NT’s security and management committee.

“But it was not implemented, which is unacceptable,” he said.

“I am sorry this did not happen.”

Mr Gunner said Territorians had a right to know if they had visited a location where a positive case had also visited.

“The messages are intended to inform someone if they have been to an exposure site and [need to] monitor for symptoms,” he said.

The government employee responsible for overseeing the project at the NT emergency operation centre had been stood down from the role.

Mr Gunner said the system had now been set up and messages would be sent from 3pm on Friday.

It came as police investigated an alleged black market in rapid tests promoted on social media.

Acting-commissioner Michael Murphy said people were allegedly on-selling government supplied RATs for a profit.

Meanwhile, an outbreak in Yuendumu and Yuelamu, about 295 kilometres north-west of Alice Springs, has grown to 43 cases.

“It continues to be confined to a handful of households,” Mr Gunner said.

A lockout of unvaccinated people will be extended until next Thursday.

Mr Gunner said Yuendumu’s vaccination rate continued to rise with 78 per cent of residents 16 and over given one jab of a COVID-19 vaccine, and 58 per cent fully vaccinated.

“This is a solid jump over the last few days, which is encouraging,” he said.

-AAP