An Australian volunteer on board a boat carrying aid to Gaza says he feared for his life after a drone strike on the vessel.

Gold Coast-based Yusuf Omar, the founder of an online media company and a former CNN journalist, described the survival of the six passengers and crew on the Portuguese-flagged ship on Tuesday as miraculous.

"I felt the heat of a massive ball of flames. I was sleeping on the top deck as it hit," he told AAP from Tunis hours after the explosion.

"I was shocked and terrified for my life."

The Global Sumud Flotilla said the main and storage decks were damaged by fire from the strike, which Tunisian authorities deny took place.

The flotilla is part of an international effort to deliver air to Gaza through civilian boats with several high-profile celebrities joining

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