Two people, including a teenager in a critical condition, have been taken to hospital after the boat they were on capsized on Friday afternoon.

Four people were onboard a vessel that overturned off the coast at The Cut near Bunbury, 2.5 hours south of Perth , about 1pm.

WATCH THE VIDEO ABOVE: Water emergency as boat capsizes.

A teenager was taken to Bunbury Regional Hospital under priority conditions, St John WA told 7NEWS.

A second patient was taken to the same hospital under normal road conditions.

Two others on the vessel were not hurt, it is understood.

Water police, local volunteer sea rescue crews, and the RAC Rescue Helicopter were among those who raced to the scene of the water emergency.

It is not yet clear how the vessel came to be in trouble but 7NEWS has seen footage o

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