HONG KONG (AP) — Thousands of passengers were being held Wednesday on a cruise ship in Hong Kong for coronavirus testing after health authorities said nine passengers were linked to a recent omicron cluster and ordered the ship to turn back.

Authorities forced the Royal Caribbean’s Spectrum of the Seas ship, which began sailing on Sunday on a “cruise to nowhere,” to return a day early on Wednesday, according to a government statement.

The ship was ordered to return after nine passengers were identified as close contacts of an infected patient who was linked to a new omicron cluster.

The ship returned to Hong Kong on Wednesday morning and passengers were being held onboard while they awaited testing.

Royal Caribbean said in a statement that the nine guests were immediately isolated and had all tested negative, and that the company was working closely with authorities to comply with epidemic prevention policies and regulations.

Over the past week, Hong Kong authorities have locked down several residential buildings linked to emerging omicron clusters as it sought to prevent the spread of the coronavirus variant in the city.

The clusters emerged after several Cathay Pacific crew members broke isolation rules and dined at restaurants and bars in the city, before testing positive for the omicron variant.

Royal Caribbean said guests who were on-board the affected ship would receive a 25% refund on their cruise fare. The ship’s Thursday sailing was also cancelled as the crew has to undergo mandatory tests, and those guests will receive a full refund.

Meanwhile Hong Kong authorities have announced a two-week ban on inbound passenger flights from Australia, Canada, France, India, Pakistan, the Philippines, Britain and the U.S. The ban will take effect Jan. 8 and continue until Jan. 21.