Man dead, two more rescued after boat capsizes off Perth coast

One man has died and two more have been rescued after their boat capsized off the Perth coast.

Police said a full emergency response, including a rescue helicopter and water police, was deployed after two men aboard another vessel saw the upturned boat about 10 nautical miles off the coast of the northern Perth suburb of Alkimos.

While two of the three men were rescued, the third was already dead by the time crews arrived.

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Police said it was believed the three men were fishing when they ran into trouble.

"This is still subject to an ongoing investigation and subject to report to the coroner however, interim information received would indicate that the vessel was anchored," Senior Sergeant Jamie Brennan told media on Friday afternoon.

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"They came to some difficulty and shortly thereafter, the vessel capsized."

He said the two survivors had been wearing life jackets, and that an orange emergency flare had been deployed.

"There was a fair bit of swell out there today," Brennan said.

"The seas can be quite an unforgiving environment."

Police said the two survivors appear to be uninjured.

The capsized boat has been towed back to shore, where it has been seized as part of the investigation into the incident.