The United States' Centres for Disease Control and Prevention (CDC) has added Singapore to its list of "very high" risk travel destinations.

Under its travel notices, the CDC raised Singapore to Level 4, its highest risk category, from Level 3 previously. The notice cited: "Level 4: Very High Level of Covid-19 in Singapore." It asked US residents to "avoid travel to Singapore".

"If you must travel to Singapore, make sure you are fully vaccinated before travel.

"Because of the current situation in Singapore, even fully vaccinated travellers may be at risk for getting and spreading Covid-19 variants," the CDC said.

It urged travellers to "follow recommendations or requirements in Singapore, including wearing a mask and staying six feet (1.83m) apart from others". Singapore reported 3,994 new Covid-19 infections yesterday.

The Republic recently announced the expansion of a quarantine-free travel scheme for travellers vaccinated against Covid-19.

The first flight under the expanded Vaccinated Travel Lane (VTL) scheme will touch down in Singapore today, in the next step of the reopening of the country's borders. SQ329 operated by Singapore Airlines (SIA) is expected to land at Changi Airport at 5.55am today. It was to depart from Amsterdam in the Netherlands at 11.15am local time (5.15pm Singapore time) yesterday.

Meanwhile, a VTL flight from the United States, SQ23, was expected to depart from New York yesterday evening local time, and land in Singapore at 5.20am tomorrow.

The Netherlands and the US are among eight of the latest countries the Republic has opened up VTLs with. The other countries are Canada, Denmark, France, Italy, Spain and Britain. Singapore had earlier opened up VTLs with Germany and Brunei on Sept 8. It will jointly launch VTLs with South Korea on Nov 15.