Tonga's first lockdown due to a case of Covid-19 has begun, and the streets of Nuku'alofa are quiet.

Tonga's main island Tongatapu began a seven day lockdown after the kingdom recorded the arrival of its first case of Covid-19 on a flight from Christchurch last week.

The lockdown begun just after midnight, with only essential services allowed to open, which include banks and the market. Gatherings are not allowed, except small numbers at funerals, and alcohol cannot be sold.

RNZ Pacific correspondent Kalafi Moala said he drove across town during the day and it was very quiet.

"Today looks like a very solid Sunday - there is nobody around.

"A few of the stores are open but everything else is closed down and there are police checkpoints in some of the key parts of Nuku'alofa."

Police were checking people wore masks and that they carried vaccination cards if they went into sites where the cards are a condition for entry.

Moala said there had been a surge of vaccinations since Friday, which propelled Tonga past its 90 percent vaccination target.

About 7000 people were vaccinated between Friday and Monday, which is about 7 percent of the population of Tonga.

Former senior public servant Lopeti Senituli told RNZ some stores had opened and people were out, but schools, government departments and churches were shut.

Senituli said Tonga held a practice lockdown 20 months ago, so people knew what to expect, and there was already a night-time curfew in effect to combat law-breaking.

"We have lived through this before. Before this lockdown we were locked down from midnight till 5 in the morning.

"So that was normal every day, especially for the kava drinkers - they had to rush home before midnight and sometimes they would sleep over wherever the kava club is, until the time when they could come back home.

"So it is something people have adapted to I think," Senituli said.

The man who tested positive for Covid-19 has been in quarantine since arriving on a repatriation flight on Wednesday.

University of Otago public health researcher Dr Viliami Puloka is in Tonga supporting the vaccine rollout.

He told Morning Report there was no evidence the virus had spread into the community.

"The concern is the people that were sitting together coming on the flight, and those who were sitting in the bus transporting to the managed isolation. They have tested those people and everyone who came on the flight, and it all came [back] negative.

"All the front line workers who were receiving the [travellers] have had their tests as well, and also been isolated, but all the tests from the frontline workers came up negative, so that's good news."

He believes Tongan authorities are likely to take a cautious stance toward the possibility of reopening the borders in the future, to protect the small country from Covid-19 entering the community.

"The infrastructure here would not be able to manage any big outbreak, any community transmission, unlike New Zealand and other places. That's a message I hear from people in the Ministry of Health and the Government in general - they would be very reluctant to do that.

"And therefore they are trying to encourage people to do things so they don't have to rely on goods and things coming from outside. Like in this lockdown you are allowed to go and work in the garden, you are allowed to go fishing... they've been encouraging people to grow their own crops.... there's plenty of local food."

Tonga is less reliant on its tourism industry than other Pacific Island nations like Fiji, so there was less pressure to reopen the borders for tourists, Puloka said.

"Our best bet is to keep it out, stamp it out."