The amber alert, the lowest level on a three-tier system that also includes red and black alerts, indicates signs of a threat in a country.
It means travellers should monitor the situation and exercise caution.
France, Thailand, parts of Japan near the Fukushima Dai-ichi nuclear power plant, Egypt, the Philippines and Bangladesh are among the 20 countries or regions currently covered by an amber OTA.
“[Travellers] should avoid large gatherings of people and pay attention to local announcements on the latest situation,” the spokesman added.
Hongkongers requiring assistance may call the Immigration Department’s 24-hour hotline at (852) 1868, or use the 1868 hotline via the Immigration Department mobile app.
They can also contact the Chinese embassy in the UK at (44) 7536174993, or send a message to the 1868 WhatsApp or WeChat assistance hotlines.
The violence erupted in Southport, a coastal town in northwest England, and spread to several other regions over the past week, after a stabbing attack on July 29 that killed three children and injured 10 others.
British citizen Axel Rudakubana, a 17-year-old British citizen born to Rwanda parents, was arrested at the scene and charged with three counts of murder and 10 counts of attempted murder.
Misinformation circulating online falsely identified the suspect as Muslim and an immigrant, fuelling anger among far-right supporters.
Protesters, including local far-right demonstrators, have clashed with police and caused damage across the country since the stabbing incident.
Local media reported that some demonstrators hurled bricks at police and mosques, and set fire to property.
More than 370 people have been arrested across the country for their role in the protests as of Tuesday.
The attack on July 29 at a summer dance class in Southport shocked the nation. While knife crime is a long-standing problem in the UK, mass stabbings are rare.
UK Prime Minister Keir Starmer blamed the ensuing violence on “far-right hatred” and pledged to put an end to the disorder.