MOBILE, Alabama (AFP) - The stricken Carnival cruise ship Triumph arrived back in port late on Thursday, ending a nightmarish ocean voyage for some 4,000 desperate passengers and crew after it lost power over the weekend.

At a little after 0300 GMT (11am Singapore time) Friday, the crippled ship inched into the port in Mobile, Alabama, after being towed here by a flotilla of tugboats.

Families cheered from dockside and waved to relatives who stood on the deck of the darkened ocean liner, which has been likened to a massive hulking skyscraper on the open water.

Carnival CEO Gerry Cahill told reporters shortly after Triumph's arrival here that the first order of business would be to apologise to the passengers for their ordeal.

"I would like to reiterate the apology that I made earlier, because I know that the conditions on board were very poor and it was very difficult, and I want to apologize again to subjecting the guests to that," he said. "We pride ourselves in providing our guests with a great vacation experience, and clearly we failed in this particular case."

What was supposed to have been a pleasurable excursion in the Gulf of Mexico turned into a hellish ordeal after an engine room fire on Sunday left the ship without the power needed to prepare meals or flush toilets.

A flotilla of tugboats was pulling the massive ocean liner into port, in an operation that took longer than anticipated because of a delay when the towline for one of the boats snapped and had to be replaced.

The Miami-based operator said cruises on the ship, which left the port of Galveston in Texas on Feb 7, have been halted until at least mid-April.

Some of the passengers on the Triumph, which is operated by Florida-based Carnival Cruise Lines, signalled news media helicopters with "SOS" messages scrawled on sheets, desperate to flee the stench and mess that they had endured for four days.

Several travellers waved home-made flags fashioned from bed sheets to express their distress. One sign read: "S.O.S." Another: "We R Not OK." At one point, a group lay on the sundeck and spelled out the word "help" with their own bodies." Other passengers joined by telephone described a stomach-churning ordeal and sent photographs showing grim hygiene conditions.

The Triumph had originally been scheduled to return to port early Monday after a weekend stop in Cozumel, Mexico.

Carnival officials said earlier on Thursday that even after Triumph docks, it could be another several hours before all of the passengers disembark, and some of the travellers face long bus or car rides back to Texas or other destinations far from this Gulf port city.

Carnival officials said earlier on Thursday that even after Triumph docks, it could be another several hours before all of the passengers disembark, and some of the travellers face long bus or car rides back to Texas or other destinations far from this Gulf port city.

Ms Jamie Baker, a passenger from Texas told US television that pipes had burst, the toilet system was backed up and cabins had dirty water sloshing around in them.

Ms Baker complained that passengers had to wait in line for up to four hours for meals she described as "basically bread" or in her case, skimpy sandwiches of tomato and mayonnaise.

"Sanitation is a huge problem. Food is very sporadic," she said.

Mr Terry Thornton, senior vice-president of marketing at Carnival, blamed the slow pace of the disembarkation on the fact that, with power still being off, there was just one functioning elevator aboard the disabled ship.

Carnival has cancelled several upcoming sailings of the Triumph and has offered financial compensation and discounted future travel for the distressed passengers.

Mr Thornton said advance teams of custom officials were already onboard the ship to speed up the process of clearing passengers. He said Carnival has snapped up hotel rooms throughout the city of Mobile to accommodate weary travellers and the relatives who have travelled to meet them.

In January last year, another Carnival ship, the Costa Concordia, ran aground and sank off the Italian coast, killing 32.