People Trapped After WA Jetty Collapse

At least three people have been caught up in a dramatic incident on Rottnest Island when a jetty collapsed as they were fishing.

Part of the Army Jetty gave way just before 6.30am on Wednesday at Thomson Bay, near the old barracks, while five relatives were fishing.

Sergeant Phil Cartledge told AAP the boy was initially unconscious and was being held up in the water by his 48-year-old mother before a yacht tender took him back to shore.

Image: Ian Jones

The mother swam to shore but a 63-year-old woman had to be freed by emergency crews after her foot became trapped.

"We had to jam the slab up to free the woman, then swim her (100 metres) to

shore," Cartledge said.

Two men were also on the jetty but did not fall into the water.

The women were flown to Royal Perth Hospital where they are being treated for lower leg injuries, believed to be fractures, and remain in a stable condition.

The boy was airlifted to Perth Children's Hospital with head injuries and a fractured ankle, and is also in a stable condition.

Cartledge said two family members lived in Australia and the others were from the United Kingdom.

Opposition leader Mike Nahan said it could have been worse if the collapse happened during school leavers celebrations.

Nahan said the former government planned to demolish the jetty and replace it with a marina, but the plans were shelved by Labor in favour of tourism marketing spending, including quokka selfies with tennis champion Roger Federer.

"It spent the money trying to attract people to the island rather than making sure the island's infrastructure was safe for them to come - serious mismanagement," he told reporters.

A Rottnest Island Authority (RIA) spokeswoman told AAP rangers had closed off the area to the public and a structural assessment would only commence once the area was deemed safe for workers.

Fisheries Minister Dave Kelly said the Department of Transport would likely investigate, while Premier Mark McGowan said other island infrastructure should also be assessed.

A 2014 report estimated it would cost about $3 million to replace the jetty, saying the Main, Army and Stark jetties had "maintenance issues, which need to be addressed to ensure their ongoing structural integrity, requiring substantial investment".

The RIA's 2017-18 budget for repairs and maintenance, excluding a roofing project, was increased by $536,000 compared to the previous year.

Built in 1906, Army Jetty was initially named the Excursionist Jetty and used as a passenger terminal, but was later upgraded for military purposes leading up to and during World War II.

It was used for ferry berthing before the Main Jetty was built in the 1960s.

Feature Image: Ian Jones