As confirmed cases of Zika virus in Singapore rose to 82 on Tuesday, the United States and South Korea joined a growing list of countries warning pregnant women or those trying to get pregnant to avoid travelling to the city-state.

The mosquito-borne Zika virus, which has caused explosive outbreaks in the Americas and the Caribbean since late last year, poses a particular risk to pregnant women because it can cause microcephaly, a severe birth defect in which babies are born with abnormally small heads and underdeveloped brains.

On Tuesday, the US Centers for Disease Control and Prevention (CDC) said it had added Singapore to its interim travel guidance list.

“Women who are pregnant should not travel to Singapore. If you must travel, talk to your doctor first and strictly follow steps to prevent mosquito bites during your trip,” the CDC said on its website.

“Pregnant travellers returning from Singapore, or who have had possible sexual exposure, should be offered testing for Zika virus infection,” the statement said, adding that women planning to conceive should wait at least two months after their return.

The CDC also warned that sexual transmission of Zika is possible, and that travellers should take steps to prevent mosquito bites for three weeks after their return from Singapore to ensure they do not spread the virus to uninfected mosquitos.

South Korea advised pregnant women and those planning pregnancy to postpone trips to Singapore, and said those returning from the country should avoid pregnancy for two months. South Korean travellers will receive text messages with the warning when they arrive in Singapore.

Earlier, Australia and the UK also issued travel updates urging their citizens to protect themselves from mosquito bites when travelling to Singapore and for women to defer travel plans if pregnant.

Taiwan's Centre for Disease Control raised the travel notice level for Singapore to Level 2 for the Zika virus. It also advised pregnant women not to travel to the city-state and other travellers to take precautions against mosquito bites.

Singapore reported its first case of locally transmitted Zika last Saturday. The number of confirmed cases has since risen to 82, with transmission appearing to occur outside of the original cluster.

Neighbouring Malaysia and Indonesia have stepped up protective measures, introducing thermal scanners at airports and border checkpoints with Singapore. 

The outbreak and advisories come as the tourism industry in one of the world's busiest travel hubs already faces weak global economic growth. Singapore's Tourism Board said it was premature to consider any impact on the sector, adding it remained a "safe travel destination".

More than 55 million people pass through Singapore's Changi airport every year. In the first half of this year, tourism arrivals topped 8 million, around 1 million more than a year earlier.