Only hours after Judy Bailey completed the Tongariro Crossing, the volcano awoke from its century-long slumber...

The threat of volcanic eruption has done wonders for tourism in Iceland.

Heavy rain has caused a lahar - a stream of ash and mud - from Tongariro's northern slopes to close a section of Highway 46 near Lake Rotoaira, but a GNS volcanologist says this is completely in keeping with the after-effects of eruptions.

Scientists say there is still a 50/50 chance that Mount Tongariro could erupt - and it could be at any time.

Interest in the Tongariro Alpine Crossing has gone "through the roof" since Mount Tongariro erupted on Monday night.

Former TVNZ newsreader Judy Bailey says good timing probably saved her from near disaster.

Locals have criticised the response to last night's Tongariro eruption as too slow but authorities have defended their procedures, saying they quickly established there was no immediate risk and put plans in place.

Rotoaira local David Bennett was concerned by the lack of communication between the authorities and National Park residents when Mt Tongariro erupted about 4km from his home last night.

Locals in the Central North Island area share their experiences and stories as Mt Tongariro erupted late last night.

The aviation colour code around Mt Tongariro has been downgraded from red to orange, but the volcanic alert level remains at 2.

Mt Tongariro is one of three major volcanos in the central North Island, sitting alongside mounts Ruapehu and Ngauruhoe.

Mt Tongariro erupted for the first time in over a century at 11.50pm on August 6, 2012, raining ash onto many Central North Island roads and homes.