The Carnival cruise ship slowly making its way back to dry land has suffered another setback as a tow line snapped, setting the ship adrift once again.

Passengers on-board the Carnival Triumph have described overflowing toilets, sewage backed up in showers, scarce food and people getting sick, bringing the scene into sharper focus after a week at sea.

Carnival Triumph being towed to port. Photo: Getty Images

What began as a four-day voyage in the Gulf of Mexico has turned into a nightmare, not at all the luxury cruise touted in brochures.

Passengers were expected to make it to shore on Friday (AEDT) - only to then face an hours-long bus ride or other travel hassles to finally get back home.

Frustrations with the cruise line were simmering on and off the ship, as passengers and their relatives questioned why it has taken so long to get back to dry land after an engine-room fire disabled the ship on Sunday.

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"There's poop and urine all along the floor," Renee Shanar, of Houston, said from her mobile phone aboard the ship. "The floor is flooded with sewer water ... and we had to poop in bags."

The ship was in sight of the Alabama shore on Friday morning (AEDT) when the tow line broke.

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Until the repair is complete, the ship is "dead in the water and when they reconnect safely, they then proceed on their way", Coast Guard Petty Officer William Colclough said.

The 14-storey ship still has to negotiate a tricky shipping channel before it could dock. Before the line broke, the ship was travelling about 8km/h.

Television images from CNN showed passengers with signs of "Help" and "I love you" hanging from their cabin rooms.

Others walked around the deck, some waving to the helicopters flying above. People in boats, presumably officials from Carnival, the Coast Guard and Customs, have boarded the ship.

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Shanar, who is on the ship with her husband, said the couple had a cabin with no windows, so they have been sleeping outside for days. She said the food has been distributed on the ninth floor, and some of the elderly have needed younger people to bring it to them. They were initially given only cold cuts, such as turkey and vegetable sandwiches. Then another cruise line dropped off hamburgers and chicken sandwiches, but the line for that fare was nearly four hours long.

"And then people started getting sick from the food," she said.

The company has disputed the accounts of passengers who describe the ship as filthy, saying employees are doing everything to ensure people are comfortable.

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Terry Thornton, senior vice-president for Carnival Cruiselines, said they received an extra generator that allowed them to serve hot food on the ship on Wednesday night, and that the food services will be fully operational when they are docked.

"This is going to be a long day," Thornton said. "There is no way we can speed up the process."

In pictures - Carnival Triumph: The nightmare cruise ship

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