SYDNEY - A group of Australian surfers have recounted a terrifying ordeal in Indonesia after a tsunami "like a million trucks" left them scrambling from their burning boat and tossed them around in killer waves.

The nine were on board the MV Midas when a massive 7.1-magnitude earthquake triggered a tsunami off the Mentawai islands, smashing the neighbouring Freedom III into their 70-foot (21-metre) motor cruiser and sparking an engine fire.

"It looked like a million trucks coming down the highway, that's how fast it was coming," one of the men, Jethro Jones, told the Sydney Morning Herald.

A wall of water five metres in height and half-a-kilometre (500 yards) across slammed the Freedom III into the Midas, unleashing a fireball that took less than 30 seconds to engulf the lower deck.

Everyone but Robert Marino managed to jump overboard, explained James Finucan, adding that he thought the lawyer "had died for sure".

But Marino, trapped below decks, managed to squeeze through a porthole barely bigger than a human head, twisting desperately to free himself as noxious fumes and intense heat enveloped the stricken boat.

"I thought, 'I can't give up'," Marino said.

"I was left with two choices: you die or you do what you can to survive. I didn't want to die."

Then a tidal surge like a "superfast river" swept seven of the nine into a jungle swamp where they spent the next 40 minutes being tossed with debris onto the shore and sucked out to the ocean again, clinging to whatever they could.

Two others were dragged out to sea where they were pulled to safety aboard the Freedom III, watching in horror as the Midas "kept exploding and kept going bang, bang, bang", said another of the survivors, Jimmy Black.

The tsunami's death toll topped 300 on Thursday, with fears mounting for another 379 people still missing.

Entire villages had been washed away and hopes were fading that the missing had simply run into the hills.

The disaster coincided with the eruption of Java's Mount Merapi volcano which killed at least 32 people on Tuesday, driving some 42,000 people from their homes.