Under the vaccinated travel lane (VTL) programme, Singapore allows quarantine-free entry for fully vaccinated travellers arriving from certain countries on designated flights or buses. The travellers have to undergo regular testing.

About two dozen countries are listed in the programme including Australia, India, Malaysia, Britain and the United States.

But no new tickets would be issued for people hoping to arrive from any of those countries from Thursday to Jan. 20, the government said on Wednesday.

"Our border measures will help to buy us time to study and understand the Omicron variant, and to strengthen our defences, including enhancing our healthcare capacity, and getting more people vaccinated and boosted," the health ministry said in a statement.

The government said it would also reduce the VTL quotas and ticket sales for travel after Jan. 20. For flights, the total number of VTL tickets would be capped at 50% of the previously allocated quota.

Travellers already holding tickets on VTL flights or buses and who meet all other requirements can still travel under the programme.

The government also urged people arriving in Singapore to minimise their social interactions, avoid large gatherings and eating out for seven days even if their tests, which they have to take every day for the week, are negative.

Singapore has confirmed 65 imported Omicron cases, along with a handful of local cases. But the government said it has been able to limit onward community transmission.

The health ministry said on Monday it had found a suspected Omicron cluster in a gym.

(Reporting by Aradhana Aravindan in Singapore; Editing by Ed Davies, Robert Birsel)