Efforts to locate missing Rescue 116 crewmen Paul Ormsby and Ciaran Smith, will intensify once more this weekend.

A major underwater search is taking place, with more than 150 divers traveling to Mayo to assist in the operation.

It is over a month since the Coast Guard helicopter crashed in the sea near Blackrock Island.

The search of waters around the island will last two days.

It's thought to be the biggest underwater search in the history of the state.