A group of Tongan seasonal workers stranded in New Zealand because their flight home this week has been cancelled are better off staying in Aotearoa, says an RSE scheme official.

The flight was scheduled to leave Auckland on Thursday.

Air New Zealand postponed its repatriation flight to Tonga because of the volcanic ash clouds from the Hunga Tonga-Hunga Ha'apai volcanic eruption last weekend.

Seventy Tongan seasonal workers were among those booked on that flight, with majority of the labourers returning home after as long as two years. Some have not heard from their families since Saturday.

There are 800 Tongan labourers in the Recognised Seasonal Employers Scheme.

RSE scheme liaison Sefita Hao'uli said the workers fear for their families' safety and are "disappointed they won't be seeing their loved ones anytime soon."

"But they should also be aware that this is something that was unexpected," Hao'uli said.

"In the interest of everybody's safety and making sure that not only are they safe on this end but if and when they do go back home, they will also be safe and not become a burden to their families."

They have to make a decision that best suits them, Hao'uli said.

"The repatriation flight is now delayed indefinitely. It is also very likely that the incoming flight on the 25th of January which was supposed to bring workers is also going to be delayed indefinitely."

Air NZ is yet to confirm the status of that scheduled flight from Tonga next Tuesday.

In a statement, the airline said they are monitoring the situation closely and their hearts go out to the people of Tonga.

"It is the airline's decision that we are following through. If the airline doesn't deem it fit to fly, there will be no flight. Everybody accepts that," Hao'uli said.

There is significant damage to the western coast of Tonga's main island, Tongatapu

The New Zealand High Commission said the damage is centred along the western coast, where there are many resorts, and the waterfront of the capital, Nuku'alofa where a thick layer of ash remains blanketed.

Tongan authorities are working to establish communication with smaller islands "as a matter of priority", the commission said.

Hao'uli said they are working with the employers, airline and immigration officials to accommodate the stranded Tongan labourers.

"We met with the employers and they are happy to act in the best way possible to make sure the workers are not going to be left high and dry. That means that if they wish to remain and continue to be employed, that will be the case.

"We don't want to see our workers go and make things any worse in Tonga place than it is already. There could be food and water issues, there could be some health issues and don't forget we got Covid to contend with.

"Given the multiple issues that they have to face, I think it's very important to take a more cautionary approach," Hao'uli said.

Some workers have already cancelled their visas, Hao'uli said, with majority of the 70 stranded holding bridging visas which enables them to stay in New Zealand "until such time there's a flight available for them."

"In cases like this when they were ready to go and now the flight is cancelled, Immigration NZ has been accommodating enough to say 'this is beyond your control,' and if the workers wish to remain in the country and work until later, then their visa could be extended."

This degree of flexibility can help stranded seasonal workers in New Zealand, Hao'uli said.

Is is safe to travel to Tonga?

"What we would really like to know is what's the situation in Tonga and whether it's safe for our workers to be able to go home?

"We need to ensure that everything is looked into otherwise we might end up contributing to the difficulties back in Tonga."

Hao'uli said by insisting on going well ahead when "perhaps they should wait until it's a lot more clear as to what Tonga needs and get those needs taken care of before they board the flight."