In this image from video, provided by the California National Guard, a helicopter carrying airmen with the 129th Rescue Wing flies over the Grand Princess cruise ship off the coast of California Thursday, March 5, 2020.

Vice President Mike Pence said Friday that 21 people aboard the Grand Princess cruise ship moored off the coast of California have tested positive for COVID-19.

The ship will be brought to a non-commercial port, Pence said, and everyone aboard the ship will be tested. He did not say which port the ship will go toward or when it is expected to arrive.

Of the 21 people who tested positive, he added, 19 are crew members and two are passengers. Pence said health officials tested only 46 people aboard the ship.

"We are instituting the strongest testing protocols to ensure that not only those on board receive the treatment that they need, but that the American people can be confident there will be no erosion in our preventative efforts to keep the coronavirus from spreading throughout our country," Pence said Friday alongside other members of the White House COVID-19 task force at a news briefing.

There are more than 3,500 people aboard the ship, the operator, Princess Cruises, which is owned by Carnival Corp., said in a statement.

The ship was due to arrive in San Francisco on Wednesday, California officials said on Thursday, but was held at sea, off the coast of California while testing was conducted. The California National Guard delivered test kits to the ship by helicopter on Thursday.

The ship, which was on a two-week voyage to Hawaii, was ordered to return early to San Francisco, California, Gov. Gavin Newsom said Thursday, adding that passengers and crew developed symptoms. A spokesman for the Centers for Disease Control and Prevention said that three passengers who were previously on the ship have tested positive, including one who has died.