Hong Kong reported 43 new cases of coronavirus on Saturday, the highest daily rise in more than three months. Of these, 36 were transported domestically – including 13 that could not be tracked.

Traveling without quarantine has been a huge problem for both destinations, with strict access regulations in place for months. When the coronavirus pandemic struck, both governments closed borders and barred entry for most non-residents and short-term visitors. In Hong Kong, returning residents are required to undergo a 14-day quarantine and wear an electronic bracelet to track their location.

How the bubble was supposed to work

On Sunday, the bubble was to begin with one flight per day to each city, with a quota of 200 passengers per flight – then later set to two flights per day.

Passengers will have to meet certain criteria before embarking, such as not taking any flights within the previous 14 days, and undergoing mandatory Covid-19 testing. But they will not be subject to any quarantine or stay-at-home notification requirements or itinerary controlled, upon arrival.

However, the arrangement has always included the warning that should the Covid-19 situation deteriorate in either city, the plan will be put on hold.

The Singapore Civil Aviation Authority initially announced Saturday morning the launch of its travel bubble with Hong Kong as scheduled. But later that day, State Transportation Minister Ong Yi Kung announced that the plan had been changed.

“Given the development of the situation in Hong Kong, Minister Edward Yao and I discussed this afternoon, and decided that it would be better to delay the launch of ATB, by two weeks. We will review in two weeks the new launch date and update again,” Ong said.

Hong Kong has seen a sharp rise in coronavirus infections in the past few days, after weeks of a steady decline in the number of cases.

The city’s health protection center strongly urged the public to avoid unnecessary travel outside Hong Kong, and called on residents to avoid going out, eating out and socializing.

“The scale of the increase is very worrying,” said Chuang Chuck Kwan, head of the infectious diseases branch of the Hong Kong Center for Health Protection on Saturday.

And she warned that this new increase in cases “will be very difficult to control.”

CNN’s Jesse Young contributed to this article.