Quinns Beach in Perth's northern suburbs has been closed after a shark was spotted this morning, swimming on the wrong side of the beach's protective shark net.

The 1.5-metre shark is understood to have been removed from the enclosed area by contractors about 12:30pm.

It was initially spotted by surf life savers who were conducting a drone patrol about 8:00am today.

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A spokeswoman for the City of Wanneroo said the contractor who managed the net, Global Marine Enclosures, had no idea how the shark got inside the swimming enclosure.

She said the company had conducted a scheduled check of the nets earlier this week and no problems had been detected.

The beach has been closed and divers are inspecting the enclosure.

Contractors attempt to guide the shark out of a section of the swimming enclosure. ( ABC News: Rhiannon Shine )

Second shark net breach

The State Government-funded shark barrier extends 85 metres offshore and 300 metres along the beach north of the Quinns-Mindarie Surf Life Saving Club.

It was installed in January 2017, with Global Marine Enclosures contracted to manage it year-round for a period of five years.

Just four months ago Middleton Beach in Albany, on Western Australia's south coast, was closed when a shark was spotted inside netting installed by the same company.

Sorry, this video has expired Shark swims inside Middleton Beach nets

Authorities chased that shark out of the enclosure with a jet ski, but divers were unable to find any faults with the net.

The monitoring and maintenance program for the Middleton Beach net is carried out by a different local company, South Coast Diving Services.