A man and a woman have been found dead at sea after their boat capsized off Western Australia’s north-west coast and two other people swam to shore to raise the alarm.

Authorities were alerted to the emergency about 8.35pm on Tuesday night when the six-metre vessel overturned at North Passage near Mauds Landing in Coral Bay, about 1200 kilometres north of Perth.

Two of the four people on board the boat swam to shore and alerted bystanders about the remaining two people, who were in trouble.

Water Police coordinated an initial sea and air search on Tuesday night but the vessel and the missing pair could not be found.

The search resumed at first light on Wednesday with the help of extra resources, and a rescue aircraft spotted the boat off the reef outside the North Passage just before 8am.

Police said the man and woman were found dead on board the boat and their bodies would be brought back to shore.

The man and woman who made it to shore are receiving medical treatment in Coral Bay.

Water Police coordinated the search, which included Coral Bay and Exmouth Marine Rescue.

-ABC