LATEST: Flights to and from Gisborne, Taupo and Rotorua airports have resumed after the ash cloud from Tongariro caused cancellations this morning.
However, Hawke's Bay Airport appears to remain closed and flights in and out of Palmerston North continue to be disrupted.
Some flights to and from Napier, Gisborne, Rotorua, Taupo and Palmerston North were delayed or cancelled due to the eruption.
All flights in and out of Hawke's Bay Airport have been suspended. Check flight information for Napier airport here: http://www.hawkesbay-airport.co.nz/Flight_Information_14.aspx
Air New Zealand is the predominant airline flying in and out of Gisborne, Taupo and Rotorua. Flights to and from those areas appeared to have resumed this afternoon, according to information on the airports' websites.
Flights in and out of Palmerston North International Airport also appeared to be on schedule, apart from three arrivals from Auckland due at 2.30pm, which had all been cancelled.
The ash had affected the central plateau, Gisborne, north and southern Hawke's Bay and airlines would need to decide whether they would continue flying in and out of that area, Civil Aviation Authority meteorological manager Peter Lechner said.
"It's up to them to stay clear of the ash. If they can find a clear way through that's fine."
Flights overhead, such as from Auckland to Wellington, would not be affected. Those flights were usually at about 30 to 35,000 feet while the ash plume was about 20,000 feet, Lechner said.
If the weather patterns continue, the ash could be pushed out to sea by about 6pm tonight, Lechner said.
Air NZ said it was working closely with relevant authorities and would take guidance from the Civil Aviation Authority and MetService before deciding whether flights would go ahead.
"We will not fly through ash and are constantly taking guidance ... to ensure we can continue to carry passengers where safe routes and altitudes are available," Air New Zealand airline operations and safety general manager captain David Morgan said.
About 20 domestic flights in and out of Auckland Airport were cancelled, and 22 were delayed.
Ruapehu's two ski fields, Whakapapa and Turoa were both open for business and unaffected by the eruption this morning.
Whakapapa area manager Steve McGill said the eruption was about 20 kilometres away and the ash was being blown away from Mt Ruapehu in a easterly direction.
"The only effect that it could have would be if the wind changed and we had a bit of ash come this way, which would be no good to our snow cover obviously," McGill said.
The manager of the Chateau Tongariro, Tony Abbott, said there were about 100 skier guests at the hotel last night.
"It's business as usual here," Abbott said.
Police were hoping to access three huts on the mountain this morning to check whether anyone had stayed there, Ruapehu area commander Steve Mastrovich said.
However, the helicopter could not land on the mountain due to adverse weather.
It would instead have to land at the track carpark and search and rescue teams would have to access the huts by foot.
One hut had already been checked and it was confirmed that no-one was staying there.
Three other huts, up to 12 kilometres from the carpark, would be checked as soon as possible, Mastrovich said.
The Desert Road has been re-opened.
As of 8.45am, State Highway 46 has re-opened.
SH5 near Te Haroto Summit remains open.
Light ash reported as falling on SH1 and SH46 and as far as Napier city.
Police have closed off the dirt road to the Mangatepopo Hut at the south-western entranceway of the Tongariro Crossing, which has been declared off-limits by DoC authorities.