Singapore said it's about a delayed travel bubble in "closed discussions" with Hong Kong.

"We will announce more details when ready,” Daniel Ng, director of air transport at the Civil Aviation Authority of Singapore, said in an emailed reply to questions.

Both cities are considering additional steps to secure the arrangement and added that it is even too early to say when it is expected to begin.

After the onset of new coronavirus infections in Hong Kong, the Hong Kong-Singapore travel bubble originally scheduled for beginning in November 2010.

The travel bubble had been suspended in both cities before, when the average unlinked case of seven days in either city was five or more.

When the plan was suspended, the total number of unlinked cases in Hong Kong was 3.86 for seven days.

Dr. Leong Hoe Nam, an infectious disease specialist at Mount Elizabeth Novena Hospital , mentioned that if the number of unlinked cases is continuously below five for two to three weeks, the air travel bubble will start successfully.

In this respect, he said, the virus' incubation period has been extended to nearly 21 days.

"As an added precaution, they should ask the individual to be vaccinated. The incentive then should be no Covid-19 polymerase chain reaction (PCR) testing will be done," Dr Leong added.

"Vaccination of travellers can expedite the formation of travel bubbles in a safe manner."

Transport Minister Ong Ye Kung said last month he'd prefer not to set a target for the start of the air travel bubble.

By means of many Covid-19 tests persons traveling between Singapore and Hong Kong can prevent a long quarantine under the current protocol.

Both sides decided that each city would have a flight every day and that its per limit would be 200.

There's no travel restriction and no regulated itinerary was required.

However, travelers must meet qualifying conditions, such as staying 14 consecutive days in either city prior to their departure, and compliance with both cities' border control measures and public health standards.