In an effort to contain an outbreak of COVID-19 during its busiest travel season, the seaside resort city of Sanya in southern China shut down its public transportation system on Saturday.

Authorities declared the limitations will go into effect at 6 a.m. (2200 GMT), claiming the COVID situation was “extremely serious” and limiting people’s mobility. The potential lifting of the restrictions was not specified.

“We urge the general public and tourists to understand and give their support,” authorities said in a statement on the city government’s WeChat account.

The city on Hainan island reported 263 COVID cases for Friday. Authorities said they had detected the Omicron subvariant BA.5.1.3.

The lockdown comes in the high tourist season for the city, which is also known for its duty-free shopping and is home to several high-end hotels run by international companies including IHG and Marriott International.

The deputy mayor, He Shigang, told state broadcaster CCTV there were about 80,000 tourists in the city but that the cases were mainly among residents. People were still allowed to leave Sanya but must present two negative PCR tests taken within 48 hours to do so.

Some tourists took to social media to vent their frustration.

“My plane was supposed to leave at 9 a.m. this morning but they suddenly locked down the city … I need to go back home to start work,” said one user of the Weibo platform.

The city started imposing lockdown measures in some places on Thursday. More venues, including its duty-free malls which are popular with Chinese shoppers unable to travel abroad, were shut on Friday.