HONG KONG -- The world's biggest gambling hub Macau began its second day of mass COVID-19 testing on Monday, with banks, schools, government services and other businesses shut, but casions remaining open.

The testing of Macau's roughly 600,000 residents is expected to end on Tuesday and comes after dozens of locally transmitted cases were discovered over the weekend.

The former Portuguese colony adheres to China's "zero COVID" policy which aims to eradicate all outbreaks, at just about any cost, running counter to a global trend of trying to co-exist with the virus.

Most residents are asked to stay at home, restaurants will be shut for dine-in and border restrictions have been tightened, meaning casino revenues are likely to be close to zero for at least a week and likely the coming weeks, analysts said.

Macau's government relies on casinos for over 80% of its income, with most of the population employed directly or indirectly by the casino industry.

The latest outbreak came suddenly and has been spreading rapidly with the source still unknown, Macau's chief executive Ho Iat Seng said in a statement on the government's website.

Macau's previous coronavirus outbreak was in October last year. An outbreak in neighbouring Hong Kong this year saw more than 1 million confirmed infections, and more than 9,000 deaths, swamping hospitals and public services.

Macau only has one public hospital with its services already stretched on a daily basis.

Macau's legislature is this week due to approve an ammended gaming law which will lay the groundwork for what is required from the multibillion dollar casino operators to continue operating.

"Depending on how quickly Macau is able to get the newest outbreak under control, there is risk of delay to finalisation of the gaming law amendments and subsequent concession tender process," said Vitaly Umansky, analyst at Sanford C Bernstein.