(Updates tally, details; paragraphs 3, 6-8, 13)

HONG KONG, July 4 (Reuters) - Macau kicked off a new round of COVID-19 testing for its more than 600,000 residents on Monday, as officials in the world's biggest gambling hub raced to limit spiralling infections in the city's worst outbreak since the pandemic began.

All residents face three rounds of tests this week, in addition to rapid antigen tests, as Monday's 68 new infections took the tally in the former Portuguese colony to 852 since the middle of June. About 12,000 people are in quarantine.

Although the Chinese special administrative region has not ordered a full-scale lockdown of the kind imposed in mainland cities such as the business hub of Shanghai, Macau is already largely closed.

Non-essential government services are shut, with schools, parks, sports and entertainment facilities closed, while restaurants may only provide takeaway items.

However, Macau has allowed casinos to stay open to ensure job security in an industry that generates more than 80% of government income by employing most of the city's population, whether directly or indirectly.

Still, punters are scarce and the casinos have very few staff, with many employees staying home in line with a government directive.

Analysts said the six operators, Sands China, Wynn Macau, MGM China, Melco Resorts, Galaxy Entertainment, SJM Holding are likely to have no income for several weeks beause of the measures.

Macau had been largely free of COVID-19 since an outbreak in October 2021. It follows China's "zero-COVID" policy that aims to eradicate all outbreaks at just about any cost, but runs counter to a global trend of trying to co-exist with the virus.

Its infections are still far below those elsewhere, including the neighbouring global financial hub of Hong Kong, which has seen daily cases jump to more than 2,000 this month.

However, the services of its sole public hospital are severely stretched. The territory has an open border with mainland China, with many residents living and working in the adjoining city of Zhuhai.

About 600 Chinese health workers have come to Macau to assist coronavirus efforts. Officials have set up a makeshift hospital next to the city's Las Vegas-style Cotai strip to help cope.

(Reporting by Farah Master; Editing by Muralikumar Anantharaman and Clarence Fernandez)