A Panamanian man who watched his two companions die while surviving adrift at sea for 28 days in their small boat has sued a US cruise line because one of its ships failed to help, his attorney said on Sunday.

Attorney Edna Ramos said the lawsuit alleging negligence by Princess Cruise Lines was filed in a Florida state court on behalf of Adrian Vazquez.

The 18-year-old and his companions - Fernando Osorio, 16, and Elvis Oropeza, 31 - set off for a night of fishing on 24 February from Rio Hato, a small fishing and farming town on Panama's Pacific coast. The boat's motor broke down on the way back and the men drifted at sea for 16 days before seeing a cruise ship approach on 10 March.

Vazquez has said the men signalled for help, but the ship did not stop.

Princess Cruises has said passengers never told the ship's captain they saw a boat.

Osorio and Oropeza died later. Vazquez was rescued on 22 March near Ecuador's Galapagos Islands, more than 600 miles from where they had set out.

Ramos said the lawsuit includes testimony from two cruise ship passengers who have said they saw the disabled boat and reported it to a cruise representative on the Star Princess liner.

One passenger, Jeff Gilligan, a birdwatcher from Portland, Oregon, has told journalists he was among the first people to notice the small boat. Another birdwatcher, Judy Meredith of Bend, Oregon, has also said she saw the small open boat and through her bird-spotting scope could see a man waving what looked like a dark red T-shirt.

Meredith has said she told a Princess Cruises sales representative what she and Gilligan had seen and he assured her he had passed the news on to the ship's crew. The two passengers said they put the sales representative on one of the spotting scopes so he could see the small boat for himself.

Princess Cruises is owned by Carnival - the same corporation behind the operator of the Costa Concordia which capsized this year.