Four French tourists survived an eight-metre fall into a river after a cable on a Lake Waikaremoana Track bridge gave way on Thursday.
A cable on the Hopu Ruahine bridge on the track "released" about 1pm, Department of Conservation operations manager Mike Slater said, "and that's where people that were on the bridge have slipped off and fallen".
The tourists who were on the bridge at the time fell into the river below. "Fortunately, other than some scratches and a little bit of bruising, they are not seriously injured. That's a very fortunate outcome."
Mr Slater said a full investigation was under way to work out what had occurred. The bridge spans about 65m across the river and is 8.5m above the water at the start and end of the track. The bridge is rated for 10 people at one time.
"We've got a very comprehensive and robust asset management system," Mr Slater said.
That included an inspection programme. "Those bridges every six years are inspected by an engineer who would give a full engineering inspection. Every second year between that time they would be inspected by a qualified departmental inspector and every 12 years they undertake a full load testing."
The bridge was inspected in September last year, and was fully inspected by an engineer 18 months ago, Mr Slater said. "An event such as this is an extremely rare occurrence and we just need to understand in this particular case exactly what did happen."
The bridge was now closed.
An engineer was on site and would carry out an engineering inspection to understand what failed in terms of the bridge's construction.
"We will also look to undertake an investigation so we understand the detail of our management regime over time, including those inspection programmes."
Labour's conservation spokeswoman Ruth Dyson said the Government had to act urgently and decisively to assure trampers on all Great Walks that every bridge would be checked as soon as possible for safety.
"It is a huge relief the four overseas tourists on the Lake Waikaremoana bridge that failed landed in water and were uninjured. This is good luck not good management. Our reputation cannot rely on luck.
"The cable failure is not only extremely concerning, it leaves New Zealand vulnerable to harmful tourism reaction. This must be sorted immediately.
"Additional resources must be given to the department to carry out this work as it is obvious the pressures on them following seven years of budget cuts are causing greater strain than they can tolerate."