NUKU‘ALOFA – Air New Zealand and Virgin Australia say ash billowing out of the Hunga Ha‘apai volcano has forced them to cancel flights in and out of Tonga, stranding hundreds of people.

Air New Zealand says about 300 people were booked Monday and Tuesday to travel on two flights from Tonga to Auckland.

Air New Zealand had to divert its Auckland to Tonga flight Monday to Samoa, and cancelled the same service to the country on Tuesday.

Virgin Australia says it cancelled a Sydney to Tonga flight Tuesday, and a Tonga to Auckland flight early Wednesday morning.

The general manager of the Scenic Hotel in Nuku‘alofa, Graeme Horsley, whose own flight to Auckland was cancelled, says ash has only recently been blown across the country.

“Over the last couple of days the weather pattern has changed and the wind is actually blowing the ash and smoke across the island.”

New Zealand Civil Aviation Authority meteorologist Peter Lechner said the Hunga Ha‘apai volcano was sending volcanic ash more than 9000 metres in the air.

“The plume is stretching up to about 30,000 feet and moving off in an east to south east direction. If there’s no further eruption by later this evening, there’s no further ash expected, it will have dissipated in the strong westerly winds.”

GNS Science in New Zealand is sending vulcanologists to Tonga to help authorities observe the eruption.

The volcano, about 62 kilometres from the capital Nuku‘alofa, has been erupting since late December and has today grounded international and local flights to and from Tonga.

A GNS Science vulcanologist, Geoff Kilgour, says as long as air traffic is possible, the two scientists will make observation flights close to the vent to determine the amount of ash in the plume.

He says they will also help the Tongan authorities with ongoing monitoring.

“We’re hoping to help in any way possible with any suggestions for improved monitoring of the volcano or procedures in dealing with ash such as how they would advise the Volcanic Ash Advisory Centres.”

Geoff Kilgour of the Tongan government requested the scientists’ assistance through the Ministry of Foreign Affairs.

Grey ash “falling like rain” from the large steam and ash volcanic eruptions that are continuing in the area of Hunga Ha‘pai-Hunga Tonga, can be seen from the Tongatapu coastline, Matangi Tonga reports.

Residents at Sopu in Tongatapu and at Kanokupolu and Ha‘atafu in the western district have good views of the eruption.

Shane Egan at the Blue Banana Beach House at Kanokupolu has been photographing the eruptions since Christmas.

“It is still sending huge smoke signals into the sky in intermittent, billowing puffs.

“At times you can make out grey ash falling like rain from the back of the cloud. It is much steamier this time, without the grey-black erupting columns of the 2009 event – but then lasting much longer without any sign of dissipating.”

Egan said he is expecting to see pumice floats arriving on the beaches of Tongatapu soon.

“There has been a bit of red tidal slick in the lagoon through the week and some lifted up in the wave faces today. We expect some pumice float to arrive on the beach sometime this week with the onshore shift in winds,” he said.

Eruption of ash and tephra is slowing down, while sulphuric gas and steam continues to be emitted from Hunga Ha‘apai, Tonga’s Ministry of Lands and Natural Resources said yesterday.

The volcanic activity began about December 20 from a submarine vent three kilometres south of Hunga Tonga and 3.2km southwest of Hunga Ha‘apai, an area that is known for periodic eruptions.

“The photographs by the Tonga Navy from the eastern side of the region on January 6 2015 confirms the eruption of tephra and ash to be from Hunga Ha‘apai. There was no indication of further steam emission from the submarine vent,” the advisory stated.

There appeared to be no activity from the nearby Hunga Tonga volcanic island.