There are also three- and four-person cabins aboard.

On Tuesday, Carnival announced it was conducting "a comprehensive review" of all of its 23 ships after a fire last month that crippled one of its ships in the Gulf of Mexico, leaving passengers stranded for days while the vessel was towed back to land. Carnival President and CEO Gerry Cahill said the probe will focus on the prevention, detection and suppression of fires, engine room redundancies, and what additional hotel facilities might be provided and might run off the emergency generators.

'Human waste all over the floor'

After the problems began Wednesday, CNN was contacted by passengers describing the conditions.

Gregg Stark, who is traveling with his wife and two young children, said the conditions are deplorable.

"There's human waste all over the floor in some of the bathrooms and they're overflowing -- and in the state rooms," Stark said. "The elevators have not been working. They've been turning them on and off, on and off."

An announcement over the ship's public address system said the crew was trying to fix the problem and was working on the generators, according to Stark. A few hours later, another announcement said the problem was worse than originally believed.

"We are not allowed off of the boat despite the fact that we have no way to use the restrooms onboard," Jonathan Evans of Reidsville, North Carolina, said in an e-mail Thursday. "The cruise director is giving passengers very limited information and tons of empty promises. What was supposed to take an hour has turned into 7-plus hours."

But Thursday afternoon, Carnival told CNN that based on conversations with the ship's management team, a look at service logs "and extensive physical monitoring of all public areas, including restrooms, throughout the night, we can confirm that only one public restroom was taken offline for cleaning based on toilet overflow and there was a total of one request for cleaning of a guest cabin bathroom.

"Aside from that, there have been no reports of issues onboard with overflowing toilets or sewage. The toilet system had periodic interruptions yesterday evening and was fully restored at approximately 12:30 a.m. this morning."

'This needs to change"

Last month, an engine room fire left the Carnival Triumph crippled and adrift in the Gulf of Mexico with more than 4,200 people aboard.

That scheduled four-day cruise stretched into eight days as tugs pulled the vessel into port in Alabama. Food was scarce, and passengers sweltered in the heat with no air conditioning. People aboard also reported overflowing toilets and human waste running down the walls in some parts of the ship.

A class action lawsuit was filed against Carnival Corp. in the aftermath.

The Triumph is still undergoing repair at a shipyard in Mobile, Alabama, Carnival spokeswoman Joyce Oliva said.

"We are now focused on the lessons we can learn from the incident and also what additional operational redundancies might be available," Cahill said at the cruise industry conference this week.

Another ship, the Carnival Splendor, had a fire in 2010 due to "a catastrophic failure of a diesel generator," said Cahill, the Carnival president.

Sen. Jay Rockefeller, the chairman of the Commerce, Science and Transportation Committee, sent a letter Wednesday to Micky Arison, the chief executive officer of Carnival Corp.

"The Coast Guard has responded to a string of 90 marine casualty incidents with passengers onboard Carnival ships in the last five years," the West Virginia Democrat wrote. "It seems that Carnival has failed to take any meaningful course of corrective action after these continual incidents. This needs to change."