(Reuters) - More than 200 people on two different cruise ships have fallen ill with gastrointestinal sickness, and both vessels were to be disinfected in San Diego, the Centers for Disease Control and Prevention said on Monday.

The first ship, the Celebrity Infinity, saw 106 of its 2,117 guests and six of its 964 crew members come down with what was determined to be the highly contagious norovirus, which can cause symptoms of vomiting and diarrhea, the CDC said.

The Celebrity Cruises vessel returned to San Diego on Monday where it would undergo a thorough cleaning and disinfection, the CDC said. Passengers would disembark in stages to prevent contact with those who fell ill, it said.

The vessel departed San Diego on March 29 for a two-week cruise with stops in Mexico.

"At Celebrity Cruises we have high health standards for all our guests and crew," the company said in a statement.

Norovirus is the most common cause of acute gastroenteritis in the United States, with up to 12 million illnesses each year resulting in up to 71,000 hospitalizations and about 800 deaths, according to health officials.

As the Celebrity Infinity begins its disinfection process, a second cruise ship, Royal Caribbean Cruises Ltd's Legend of the Seas, was headed to port in San Diego with 114 of 1,763 passengers suffering symptoms including vomiting and diarrhea, the CDC said.

Two members of the 747-person crew had also fallen ill.

The cause of the illness was not yet known, the CDC said.

The Legend of the Seas was due to return to port in San Diego on Tuesday.

The ship was on a two-week cruise that started on March 30 and continues until April 14, the company, which also owns Celebrity Cruises, said in a statement.

"Royal Caribbean is undertaking direction from the CDC to inhibit the sickness and prevent further outbreaks," the company said in a blog post.

(Reporting by Victoria Cavaliere; Editing by Eric Walsh)