HONG KONG, July 5 (Reuters) - Macau reported 89 new coronavirus cases on Tuesday, taking the total to more than 900 infections since mid-June, as authorities in the world's biggest gambling hub race to contain its largest outbreak since the pandemic began.

More than 13,000 people are under quarantine in the Chinese special administrative region, which has effectively shut down to limit the spread of coronavirus.

The city's more than 600,000 residents are subject to three citywide COVID-19 tests this week, with people also required to take rapid antigen tests in between.

While the former Portuguese colony has not introduced a full scale lockdown seen in mainland Chinese cities like Shanghai, most facilities are shut and restaurants can only provide takeaway.

Only Macau's casinos have been allowed to stay open in a move to ensure job security. The government relies on the industry for over 80% of its tax revenue with most of the population employed directly or indirectly by the casino resorts.

While casinos are physically open, there are hardly any gamblers inside and very few staff working, with many employees asked to stay at home, as per the government's request.

The stringent measures come after Macau has been largely COVID-free since an outbreak in October 2021. It still has an open border with mainland China, with its economy firmly hinged to the inflow of Chinese visitors.

Macau 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.

Its cases are still far below daily infections in other places, including neighbouring Hong Kong where cases have jumped to more than 2,000 a day this month.

However, Macau only has one public hospital, whose services are already stretched on a daily basis. Officials have put up a makeshift hospital next to the city's Las Vegas style Cotai strip to help cope with the rise in cases.