HONG KONG, Oct 31 (Reuters) - Macau authorities reinstated tough COVID-19 curbs including locking down a major casino over the weekend after a handful of cases were detected, even as China announced a loosening of visa rules for visitors to the world's biggest gambling hub.

Authorities locked down the MGM Cotai casino resort owned by MGM China on Sunday, with staff and guests ordered to stay inside until Nov.

1. More than 1,500 people are sealed inside the property, the government said on Monday.

All of Macau's 700,000 residents have been mandated to take rapid antigen tests daily from Sunday to Nov 1 at least and will have to take an official PCR test on Tuesday, the government said on Monday.

The casino closure deals a blow to operators who have already been grappling with China's zero-COVID restrictions for more than 2-1/2 years, losing millions of dollars monthly.

Macau had been coronavirus-free for more than three months until last week.

The swift return of curbs marks a potential setback for industry executives and investors who were keen for a quick recovery in gambling revenues in the Chinese special administrative region.

MGM China did not immediately respond to a request for comment.

Industry publication Inside Asian Gaming, which showed images of two men who were caught and returned to the casino after attempting to run away, quoted the company as saying it would work with the Macau government on all preventive actions to reduce the risk of COVID transmission.

The prospects for travel to Macau have improved, however, with China's immigration bureau saying on Monday that mainland residents would be able to use an online visa system from Nov.

1 to travel to the former Portuguese colony.

In-person applications have been required for the past 2-1/2 years due to COVID-19 restrictions, but the bureau said that as the current COVID situation in Macau was stable and demand to visit the city was increasing, the government had decided to offer e-visas.

Shares in Hong Kong-listed Macau casinos rose between 2%-5% on Monday, cheered by easier access to the gambling hub for mainland visitors.

"This will be a great boon for Macau's return to normalcy," said DS Kim, an analyst at JP Morgan in Hong Kong.

There are still multiple COVID-19 testing requirements to enter Macau and to return to the mainland but the resumption "greatly alleviates the frictions for a Macau trip ... and could signal to many that 'it's OK' to come to Macau now."

Macau casino executives also said a decision on new licences could come as early as this week.

Macau's six casino operators - Sands China, Wynn Macau, Galaxy Entertainment, 벳이스트미니게임 MGM China, Melco Resorts and SJM Holdings - are awaiting a government decision on whether they will be granted new licences that would allow them to continue operating in 2023.

Any operators unable to secure a new licence would be required to return their premises to the government

>New licence terms will be 10 years versus 20 years previously, giving operators a shorter horizon to make back billions of dollars they have to invest under the government mandate. (Reporting by Farah Master, Twinnie Siu and Beijing newsroom; Editing by Kim Coghill, Kenneth Maxwell and Edmund Klamann)