HONG KONG, Aug 16 (Reuters) - Hong Kong"s government said it would upgrade 15 overseas places including the United States, Spain and France to "high risk" from "medium risk" by Aug. 20, meaning international arrivals from those countries will face lengthened quarantine due to a resurgence of the coronavirus. The government said arrivals from Bangladesh, Cambodia, France, Greece, Iran, Malaysia, the Netherlands, Spain, Sri Lanka, Switzerland, Tanzania, Thailand, Turkey, the United Arab Emirates and the United States would all face the new restrictions, according to a statement released on Monday. Hong Kong has some of the most stringent coronavirus entry requirements globally, with arrivals from countries considered "high risk" mandated to undergo compulsory quarantine for 21 days in a designated quarantine hotel, even those who are vaccinated. The government said there had been acute surges in the number of confirmed cases in a short period of time in many countries. "Despite large-scale vaccination programmes, many places are also experiencing resurgence of the virus, which poses enormous challenges to our local anti-epidemic efforts," the statement said. Australia will be reclassified as "medium risk" from "low risk" from Aug. 20, meaning that even vaccinated arrivals will need to quarantine for 14 nights unless they have a positive antibody test result conducted by a laboratory recognised by the Hong Kong Government, which then allows them to do a seven-day quarantine. Countries including Brazil, India, and the United Kingdom had already been classified as "high risk", but the government had largely relaxed measures for travellers from most other countries, prompting hope of increased international travel for residents and a greater number of foreign visitors. Hong Kong has largely controlled the virus with hardly any locally transmitted COVID-19 cases, but has seen a steady inflow of imported coronavirus cases over the past two months. The city has recorded around 12,000 COVID-19 cases in total. Reporting by Farah Master Editing by David Holmes Our Standards: The Thomson Reuters Trust Principles.