A Sydney man watched in horror as his wife dived from a bridge for a bungy jump but slipped from the cord and plunged into the river below.

The woman, believed to be in her 30s, was in Christchurch Hospital with serious injuries last night after the accident at midday.

Her condition has now been revised to 'stable'.

Westpac helicopter spokesman Simon Duncan said the jump went wrong when the woman, on her second bounce, slipped from her bungy harness and fell into the icy Waiau River.

"On the recoil, one of the foot straps came loose. She came out of the foot straps and landed in the water from about 6m, and unfortunately the water depth is only about 1m."

Paramedics were not sure what caused the accident. "We don't know whether it had been done up properly or whether she's a petite person who's come out of the foot strap."

Thrill Seeker Adventures was closed today following the incident.

"We opted to shut the operation down as soon as it happened," spokesman Blair Hartland told 3 News.

He said he expected the investigation by police and the Department of Labour would be completed within a day or two.

Mr Hartland said the woman undertook a 35m plunge, but he did not know how far she fell and could not confirm her shoe had fallen off.

"That's subject to the investigation which is being carried out... I can't speculate as to what the cause was."

Staff waiting in a boat below, who return jumpers to land, took the woman to a small island in the river where the Westpac helicopter arrived. A man believed to be her husband stood by stunned and upset.

Mr Hartland said his firm spent the afternoon trying to contact the woman and her family to offer support.

"The ball will be in their court as to when they're ready, but we're here to offer whatever support we can.

"We'll be doing our bit there. We're certainly not backing away from our responsibilities."

Mr Hartland said the company had suspended its entire operations, including the bungy jump, jet boating, river rafting and quad biking.

"We need to know what's gone wrong before we can safely resume."

Offering an apology and financial support would depend on the outcome of an investigation, he said.

"Regardless of that, we want to be doing the right thing. We're a good operation and we've got the customers' interests at heart and we've got the tourism industry of NZ at heart as well, so we want to make sure we do the right thing - whatever that may be."

There have been several bungy jumping accidents in New Zealand.

In May 2003, Rotorua woman Jamie Shaw, 19, suffered severe bruising after falling more than 8m into a stream after her foot slipped from the bindings during a tandem bungy in Rotorua.

In September 2000, a Taiwanese tourist, 29, received head injuries after slipping from a harness and falling 25-30m into the Waikato River.

And in 1997, Canadian Nancy Todd, 20, plunged into the Shotover River near Queenstown after part of her bungy detached as she rebounded from a jump in Skippers Canyon.