A major search operation for a missing snorkeler is underway 120km north of Perth, while a teen is in hospital with a suspected shark bite following a separate ocean emergency.

7NEWS understands a man was among a group of four off the coast of Ledge Point when he disappeared.

The alarm was raised about 3pm on Thursday.

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“A number of resources have been deployed to the area and are attempting to locate the male, including Water Police,” WA Police said.

A police helicopter has been doing a grid search off the main beach and there are vessels on the water.

There is also a large number of police on the sand.

A major search operation for a missing diver is underway 120km north of Perth, while a teen is in hospital with a suspected shark bite following a separate ocean emergency. Credit: 7NEWS

It comes as a teen is treated in hospital for a suspected shark bite.

He was injured at Catalina Beach near Mindarie, a coastal suburb in Perth’s north, about 3.45pm.

Witnesses posting to social media said they helped him into a car and he was driven by a friend to Joondalup Hospital.

It is understood he has an injury to his ankle, although it is not considered life-threatening.