A marathon runner attempting a bizarre crossing from Florida to Bermuda inside an inflatable bubble has been rescued after succumbing to exhaustion.

US citizen Reza Baluchi was pulled from the water off the coast of Florida on Saturday after triggering an emergency radio beacon.

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The US Coast Guard said they first became aware of Baluchi’s odyssey on Wednesday when personnel received a report of “a US citizen floating in an inflatable bubble”.

“Baluchi was reportedly disoriented and asking for directions to Bermuda,” officials said.

A US Coast Guard vessel arrived on the scene and urged him to halt his trip.

Baluchi, whose bubble was stocked with protein bars, bottled water, a GPS device and a satellite phone, ignored the advice and continued.

However, he finally threw in the towel on Saturday, floating 130 kilometres off the Florida coast.

The US Coast Guard scrambled an HC-130 plane and MH-60 helicopter crews from a base in Clearwater, Florida.

A rescue swimmer hoisted Baluchi from an inflatable raft where he was whisked back to land for medical evaluation.