A 2m shark has become trapped in a popular swimming spot beneath a diving platform outside Te Papa in Wellington Harbour.

A two-metre shark trapped in a popular swimming area on the Wellington waterfront has been identified as a blue shark.

It was a breed known to bite and even kill people, Te Papa shark expert Andrew Stewart said.

"You underestimate them at your peril," he said.

Alex Liu/Fairfax NZ The shark is near the jumping platform close to Te Papa.

While blue sharks appeared laid back, even small ones were muscular, with strong jaws and jagged teeth.

"If it gets hold of you it will grab a chunk."

The shark was spotted by Cafe Moana manager Ruth Belton beneath the jumping platform outside national museum Te Papa shortly after she arrived at 8.30am on Friday.

Alex Liu/Fairfax NZ The Department of Conservation has sent staff to see if the shark needs help.

Belton then alerted the Department of Conservation, and waterfront bosses and put a sign up warning people not to get in the water.

The female blue shark, which is almost fully grown, is unable to escape as it is being obstructed by blue plastic barriers, which are in place to stop stormwater discharge getting into the swimming area.

Belton said penguins had become trapped in the area before.

A DoC spokeswoman said people should stay away from the shark as it may be dangerous.

It was also good to stay out of the shark's habitat, she said.

DoC was sending staff to identify the shark and see if it needed help, she said.