A giant sinkhole has opened up on a dairy farm in New Zealand, revealing rock deposits from a 60,000-year-old volcano.

The hole, which has captured the attention of volcanologists, is as deep as four double-decker buses (20 metres or 66 feet) and is 200 metres (660ft) long.

It appeared after heavy rain near the town of Rotorua on the North Island, an area renowned for its geothermal activity.

Geologists believe that thousands of years of rain eroded underground limestone, causing the ground to collapse.

"This is pretty spectacular, it's a lot bigger than the ones I'd normally see," volcanologist Brad Scott said.


Mr Scott told TVNZ the dairy farm was situated above the crater of a dormant volcano.

The dirt in the bottom of the sinkhole was "the original 60,000-year-old volcanic deposit that came out of this crater", he said.

The farmer, Colin Tremain, said it had appeared overnight and was spotted by a worker on a morning run to handle the cows.

Similar sinkholes are common on his farm, Mr Tremain added, but this is the largest - and there was nothing he could do to stop his land disappearing.

He told Radio NZ he could "put fence around it and forget about it" but it would be a "waste of time filling it in".