Singapore Airlines Ltd. will stop flying transit passengers through Hong Kong from Saturday and budget unit Scoot will suspend transit flights from the end of April following a ban for carrying travelers with Covid-19.

The decision came after Hong Kong tightened regulations on flights arriving with infected passengers, Singapore Airlines said in an emailed statement Friday. Hong Kong has criteria for airlines that lead to two-week suspensions if breached, including if passengers fail to follow protocol related to disease control. The city gradually resumed transit flights last June after a halt.

Scoot was on Thursday suspended from flying to Hong Kong from April 16 to 29 because two passengers were confirmed to have Covid-19 on arrival. A third passenger had invalid pre-departure test results and also tested positive. Singapore Airlines was barred from April 3 to 16 due to a positive case and some passengers failing to comply with disease-control requirements.

Data from OAG Aviation show Singapore Airlines and Scoot carried 2,955 transit passengers on the Singapore-Hong Kong route in January. That compares with 51,670 passengers in the same month last year and 328,276 in 2019.

Hong Kong and Singapore are trying to form a travel bubble that would let people fly in and stay without going through quarantine. Officials on both sides this week said an agreement is being finalized and will be announced soon.

Singapore Transport Minister Ong Ye Kung said earlier this month that transit passengers wouldn’t be included in any travel bubble, and that the two-week suspension of Singapore Airlines’ flights wouldn’t affect negotiations.

Singapore Airlines said Friday that passengers on its flights from Hong Kong will still be allowed to transit through Singapore’s Changi Airport. The airline and Scoot carried a total of 222,100 passengers in the first quarter, down 96% from the same period last year.