According to Apple, they have made the ECG feature available in Hong Kong as well as 19 other countries in Europe. The countries that officially support the feature include Austria, Belgium, Denmark, Finland, France, Germany, Greece, Guam, Hong Kong, Hungary, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Puerto Rico, Romania, Spain, Sweden, Switzerland, UK, US and US Virgin Islands
This is pretty big news as previously the feature was only limited to pretty much the US. This is due to medical regulations around the world being different from each other, meaning that Apple needs to make new filings for each country and region which can take a while. In fact, it was previously suggested that ECG support for the UK could actually take years, but it seems that have arrived much earlier than expected.
Apple Watch users will need to update their smartwatches to watchOS 5.2 if they want ECG support. In addition to ECG support for those regions, the update will also bring about some minor improvements such as support for the second-gen AirPods and real-time text for phone calls.