A New Zealand volcano dormant for more than a century has erupted, sending up ash clouds, disrupting flights and closing roads.

Mount Tongariro, one of three volcanoes in the centre of the North Island, became active just before midnight local time, with reports of loud explosions, spewing rocks and steam.

The 1,978m (6,490 ft) peak is in a national park popular with hikers.

No casualties or damage have been reported after the eruption.

Witnesses described a dramatic scene as the volcano erupted.

''I saw this beautiful, big cloud and I thought: 'Gee that looks like a volcanic plume'. Just as I thought that there was a great big orange flash," truck driver Bryn Rodda told New Zealand National Radio.

"It was quite impressive."

Mount Tongariro last erupted 115 years ago, and scientists said they did not yet know if this eruption was a single event or if it signalled the start of more activity.

Experts said they were caught by surprise - they had recorded some seismic activity in recent weeks but were not expecting an eruption.

"This might just be a quiet period and we should expect it to start again at any time. So we are watching things very closely," volcanologist Michael Rosenberg told TVNZ.

Eruption activity has currently subsided, New Zealand media said. Meteorologists said the ash was blowing east towards the Pacific Ocean.

A number of domestic flights on the North Island had been affected by the volcanic activity, Air New Zealand said.

Police said highways that had been closed because visibility was affected after the eruption are now open.

Some residents in the vicinity had temporarily left their homes. Officials have not ordered an evacuation, but advised those affected by the ash cloud to stay indoors and close their doors and windows.

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