A spectacular 200m-long tomo (sinkhole) that opened up on a farm south of Rotorua in May is attracting locals and tourists after being highlighted on Google Maps.

Tumunui South farm manager Colin Tremain said about 50 people had appeared at the property wanting to view the tomo since the initial few days of viewing had taken place.

"Some clever person thought it would be a good idea to include the tomo on Google Maps so, yeah, we get a few people," Tremain said.

"They have a bit of trouble understanding that this is a working farm and there are a whole lot of health and safety issues involved. They're actually quite disappointed when I tell them they can't just wander off and take a look."

He added people were still coming, albeit sporadically, and hoped they would eventually stop.

It was Tremain who uploaded a photo of the tomo to social media not long after it was discovered – something he says he wouldn't ever do again.

"I had no idea so many people would be interested, I definitely learned the hard way with that one," he laughed.

Tremain said the tomo had not got any bigger since it opened and had been fully fenced.

"We filled it where we could including the tip that had encroached on the race way. At the top end there was a 5m-wide and 5m-deep area also filled."

He said there had been no incidents involving stock and the sinkhole.

Tomo or sinkholes are formed when groundwater dissolves underlying limestone rock. The dissolved hole enlarges to a point where it can't support the ground above it.