A main Auckland sewer line has collapsed, causing a massive sinkhole to open up, with wastewater overflow pouring into the harbour and closing the city’s beaches.

The 13m-deep hole descends to a 2.1m wide collapsed brick pipe below a private property on St Georges Bay Rd in Parnell that serves Central and West Auckland.

It is the third sinkhole in the city in three months after a section of road caved in on College Hill in Freemans Bay and another opened up on Princes St, Ōtāhuhu.

Repair work on a sinkhole on St Georges Bay Road, Parnell. Photo / Dean Purcell

Watercare’s chief operations officer Mark Bourne said the blockage may be causing sewage overflows around the network.

 “We ... are urging Aucklanders to avoid swimming, fishing and recreational activity in the Waitematā Harbour. Warning signs are being erected at all inner-city beaches.

Safeswim’s website shows all beaches west of Mission Bay in Auckland are closed. Photo / Safeswim

“We have raised black water quality pins on Safeswim.”

Safeswim’s website shows all beaches west of St Heliers are closed, affecting some of the city’s most popular beaches during the spring school holidays.

“A wastewater overflow has been detected in the area[s],” a notice on the website reads.

Bourne said the ground around the sinkhole was unstable. Watercare has cordoned off the area to keep people safe.

Watercare took “immediate steps” to address the collapse yesterday, Bourne said. It first heard about the sinkhole on Monday afternoon.

A brick pipe below St Georges Bay Rd in Parnell has collapsed. Photo / Dean Purcell

Watercare has sought advice from geotechnical engineers on how to deal with the collapse.

“Our crews worked until early this morning, removing material to strategically widen the tomo [sinkhole], stabilising the ground and preventing further material entering the pipe,” Bourne said.

A main Auckland sewer line has collapsed, causing a massive sinkhole to open up, with wastewater overflow pouring into the harbour and closing the city’s beaches. Photo / Dean Purcell

“Unfortunately, the situation has worsened with the sewer becoming completely blocked this morning, which may be causing overflows elsewhere in the network.

“Our crews on site are currently working with a large excavator to further widen the top of the [sinkhole] to remove the debris causing the blockage.”

Bourne said work repairing the pipe would get under way once the blockage has been cleared.

Raphael Franks is an Auckland-based reporter who covers breaking news. He joined the Herald as a Te Rito cadet in 2022.