Trig Rd South in Waihi is still closed after a sinkhole opened beneath the road on June 19.

The Hauraki District Council said the tomo "opened a can of worms" that they have been investigating and repairing over the past week.

Tarseal on the road collapsed on the evening of June 19, leaving an opening almost two metres wide and plunging down up to five metres.

Sinkholes typically form when rainwater dissolves and perforates through limestone, leaving sinkholes in the topsoil.

Hauraki District Council group manager engineering services Adrian de Laborde had originally said he thought the road could have been reopened by June 21.

He has since said: "Once we started to open the road and found the cavities we realised that the extent of the works was larger than originally thought."

The council now hoped the road would be open before June 30, but also noted that "wet weather looks set to hamper the final resealing efforts".

"It's likely the surface will be temporarily metalled​ until we get a drier spell of weather which will allow us to properly chipseal the area".

The council said whilst staff and contractors were repairing the road they discovered a network of "worm holes" that allowed a stream heading underground to form its own path under the road.

Adrian says water had "gone underground and carved a series of voids, possibly over years, that have eventually broken through to the surface".

​He says the area had since been fully excavated to uncover and fill all the cavities, and install a new culvert at the "new" stream level to contain the water flow.

"It was important to understand the full extent of the problem and fix it properly, rather than try and apply a band aid.

"We are comfortable that the work we have done has properly addressed any further issues at this location."

- Stuff/ JAKE MCKEE CAGNEY