Macau ordered compulsory coronavirus testing for all residents after a family of four was found to be carrying the Delta variant, breaking the city's record of over 16 months virus-free.
Over the next three days authorities plan to test all 680,000 residents at 41 testing centres, the government said.
The testing is one of a host of new measures announced after the gambling hub recorded 491 days without a single local infection, AFP reports.
Authorities are investigating whether the daughter of the family contracted the virus on a flight from Zhuhai to Xi'an in mainland China in July, Macau's leader Ho Iat-seng said.
