Geothermal activity has erupted on a busy Rotorua thoroughfare, spewing steam, mud and water and cracking the road.

The activity is coming up in the garden in the median strip on Lake Rd near the geothermally active Kuirau Park.

A Rotorua Lakes Council spokeswoman said a fumarole, a steam-driven event, appeared in a traffic island on Lake Rd this morning, which also created a crack in the road.

Geothermal activity has sprung up on Lake Rd in Rotorua. Photo / Andrew Warner

The council is currently determining the cause, but it is likely to be linked to high groundwater levels which is weather driven, it said in a statement.

Motorists are asked to avoid driving through Lake Rd. Traffic management is in place and one lane is closed while the area is being assessed.

A woman watching the action said she arrived just as the work crews did.

Traffic flows through the affected area on Lake Rd. Photo / Andrew Warner

"It had exploded and mud came out. It's cracked the road."

She had not seen anything happen like it in the area before.

Rotorua woman Liz Coppard happened to be driving past the area and spotted what she described as a bore hole that had opened up.

She said it was about 1m tall and bubbling up from the garden in the median strip of Lake Rd.

Shot of the geothermal activity taken from Pukeroa Hill. Photo / Andrew Warner

"It's right in between two power poles so not sure if that will cause any electrical issues."

She said there were about eight Infracore workers in the area with high-visibility vests on but traffic was still flowing on Lake Rd.

More to come.

Geothermal activity has sprung up on Lake Rd in Rotorua. Photo / Andrew Warner