Rockfall size of tennis court above Shotover River

A block of rock "about the size of a tennis court" fell off the section of unstable hillside above the Shotover River about midday on Saturday.

Arthur's Point residents had also reported hearing a "thunderous crash" just after 8 that morning, Queenstown Lakes District Council emergency management officer Brenden Winder said.

However, Otago Regional Council director of environmental engineering and natural hazards Dr Gavin Palmer said last night most of the material was still clinging to the hillside and none of had ended up in the river.

He said a survey team would continue to monitor the slip's movement.

It was still uncertain whether the rock would collapse into the river as a mass or crumble piecemeal, Dr Palmer said.

It was better the slip gradually fell away, rather than having large quantities landing in the river, where it could block water flow.

"Having said that, rockfalls are quite common in the Shotover and other areas," he said.

"The river erodes the rocks and takes them away."

Having the rocks fall in the gully above the river added another variable - nobody is sure if the rocks will stay there or later fall into the river.

The Shotover River between Deep Creek and the Oxenbridge tunnel was closed to all water users until further notice for safety reasons, Queenstown Lakes District Council harbourmaster Marty Black said.

"The subsiding rock above a section of the Shotover River poses danger and the area needs to remain closed," he said.

The Shotover Jet operates outside that area.

Tracks providing access to the Shotover River through the Morning Star Recreation Reserve and the Shotover Creek Conservation Area have also been closed, Department of Conservation manager of community relations John Roberts said.

The Oxenbridge Tunnel Reserve was also closed.

The Moonlight Track between Arthurs Point to Moke Lake was closed until further notice, Wakatipu Trails Trust chief executive officer Renee Bowman said.

Warning signs had been posted.

"The area is extremely unstable and anyone who chooses to ignore the caution signs is putting themselves at risk," Ms Bowman said.