Image caption The Rotorura area has seen geothermal activity like this before

A surprise geyser shot water high into the air from New Zealand's Lake Rotorua early on Monday morning, panicking some local residents.

The eruptions at about 04:30 local time (15:30 GMT Sunday) woke people living in Ohinemutu, on New Zealand's North Island.

Reports said the water reached heights of between 7m and 30m (23-98ft).

The area is known for geothermal activity, but the exact location and magnitude of the geyser are unusual.

What happened?

Locals reported hearing a series of loud thuds, followed by a spraying sound.

In a video on Facebook, Ohinemutu resident Lani Kereopa said she initially saw nothing unusual from her window "and then another one happened and I saw water spraying up out of the lake".

"I panicked, ran downstairs to wake everybody up to say 'Get out of the house, get out of the pa [settlement], the village is erupting'."

Brad Scott, a volcanologist with earth science organisation GNS Science, told the BBC: "The event today was a hydrothermal eruption, driven by steam from shallow depth in the geothermal system."

"They occur when too much steam is trapped at shallow depths" of five to 15m, he added. "The pressure grows to exceed the strength and weight of the rocks above it. Once enough pressure exists, you get lift-off."

Image caption Tourists have long been drawn to the area's geothermal attractions, like volcanic activity at this stream near Rotorua

Is it common?

The last such event in a similar spot was in the 1960s, and the last significant eruptions nearby - about a kilometre away - were in 2000 and 2001, said Mr Scott.

But the wider area is known for geothermal activity, drawing tourists to what Visit Rotorua describes as "its spouting geysers, bubbling mud pools and colourful sinter terraces".

"Ever since we have had written records there have been accounts of these steam-driven eruptions occurring. Today's event was similar to many in the past. It wasn't very large as these events go," Mr Scott said, noting that when locals drilled for steam decades ago, there were two or three such events a year.

One geyser in the region did however spurt back to life for the first time in decades last year.

Should people be worried?

Rotorua Lakes Council Geothermal Inspector Peter Brownbridge told Radio New Zealand it was akin to a cap being blown off a shaken bottle of fizzy drink.

"It must have been quite powerful to throw up a big column of water as it did, but it's nothing for people to be concerned about," he said.

It is thought that while eruptions may present a small risk to people on the lake, local residents are not in significant danger.

Is it connected to the Kaikoura earthquake?

Just after midnight on 14 November, the town of Kaikoura, in the north of New Zealand's South Island, was hit by a devastating earthquake that has left it still largely cut off.

But while both quakes and geysers are connected to tectonic activity, the timing is likely to be nothing more than coincidence.

"We cannot say they are not related. However it is difficult to think of a mechanism that would cause this, two weeks after the large earthquake," said Brad Scott.