"We had a number of tests in Katherine yesterday that weren't able to get into our laboratory in Darwin until very late in the evening," Health Minister Natasha Fyles told reporters.
"They were delayed due to the large storm that we had between Katherine and Darwin."
Ms Fyles said the weather grounded a flight that was scheduled to transport people deemed close contacts to the National Centre of Resilience quarantine facility and 300 COVID-19 tests from the Katherine area.
Severe thunderstorms dumped 35mm of rain in the Adelaide River area, northwest of Katherine, in 30 minutes on Thursday, according to the Bureau of Meteorology.
The test results are expected later on Friday, along with an update about the situation. More cases are expected.
Meanwhile, Amnesty International has apologised after its UK office issued a news release reinforcing misinformation about the Australian Defence Force's involvement in the NT's pandemic response.
A series of misleading social media posts have alleged the ADF forcibly transferred infected Indigenous people to quarantine facilities while likening them to the stolen generation.
Some traditional owners also accused military personnel of holding down people in some Indigenous communities and forcibly injecting them with the vaccine.
The posts were shared and reposted hundreds of times on Facebook and other platforms, and authorities fear they could threaten efforts to contain the NT outbreak.
Amnesty's Australia office said it was disappointed its UK office released the information.
"The additional of a headline which was not in the original statement suggesting the ADF was 'inflicting trauma' completely changed the sentiment of the statement," national director Sam Klintworth said.
It was meant to convey Amnesty's full support for the vaccination program.
"We are deeply sorry for the distress this has caused," he said.
The ADF rejected the claims, saying they were "spurious" and "deliberate disinformation".
About 85 ADF personnel are assisting authorities in and around the Katherine area, delivering food to vulnerable communities, transporting close contacts to testing facilities, and helping police at vehicle checkpoints.
The outbreak started when an infected woman illegally entered the NT in late October.
The 21-year-old lied on her border entry form before travelling from Cairns to Darwin after visiting Victoria, where she contracted the virus.
She infected a man in Darwin before the virus spread to Katherine and the Aboriginal communities of Binjari and Robinson River, which is 1000km southeast of Darwin.
The majority of the people infected are Indigenous Territorians.