Hong Kongers travelling to Singapore should stay vigilant and monitor closely the Zika virus infection situation in the city.

On Friday (Sept 02), the Hong Kong government issued an "amber" alert to remind travellers to exercise caution when they are in Singapore, which has seen 189 locally-transmitted Zika cases as of yesterday.

The health authorities had earlier advised pregnant women and women preparing for pregnancy to avoid travelling to Singapore and other regions "with ongoing Zika virus".

The Security Bureau website described an "amber" alert as showing signs of threat, while a "red" alert means there is significant threat and travellers should avoid non-essential travel when a "red" alert is raised.

Hong Kong's health authorities have been closely monitoring the outbreaks of Zika virus and would be providing advice to Hong Kong travellers visiting the affected regions with the latest Zika virus update of the World Health Organisation (WHO), a government spokesman said in a statement on Friday.

"In view of the persistent and rapid increase in the number of local Zika Virus Infection cases in Singapore and the close contacts between Hong Kong and Singapore, we consider that it is necessary to alert the public planning to travel to Singapore to be highly vigilant and pay close attention to the latest situation of Zika Virus Infection," the spokesman added.

On Aug 25, Hong Kong confirmed its first case of Zika virus, after an expatriate returned to the city from the Caribbean showing symptoms of the virus.

Investigations showed that the 38-year-old foreigner had felt sick with arthritis and redness in her eyes when she left the Caribbean on Aug 20. She arrived in Hong Kong two days later and visited a doctor the following day (Aug23). The doctor only confirmed she had been infected with the Zika virus on Aug 25 after a blood test was conducted on Aug24.

Hong Kong authorities have since stepped up routine health surveillance of inbound travellers at all entry points to the city.