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Sweeping new restrictions will be imposed across Sydney as Australia's largest city grapples with a fast-growing Covid outbreak.

Authorities reported 16 new infections on Wednesday, which brings the cluster there to 37 cases.

Sydney's 5.3 million residents will have to wear masks indoors, and many will be banned from travelling out of the city.

Officials are concerned about the "extremely contagious" Delta variant.

The cluster marks the largest rise in the number of infections in Sydney since December. For most of the year, locals have enjoyed almost no restrictions on daily life.

Due to the sharp jump in cases, the state government said new curbs would be needed.

"Please abandon non-essential activities, please don't attend social gatherings unless you absolutely must," said New South Wales (NSW) Premier Gladys Berejiklian.

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From Wednesday, households will be limited to a maximum of five visitors. Restrictions will also be put in place at dining venues, gyms, sporting arenas and other gatherings.

People who live or work in the virus hotspots – including central Sydney – will be banned from travelling out of the city.

NSW Health Minister Brad Hazzard said the virus risk had escalated to a "very real and present danger" right across Sydney.

The cluster of infections had initially centred around a shopping centre in Bondi, the popular beachside suburb and famous tourist destination in the city's east.

image copyrightGetty Imagesimage captionDrive-in Covid testing sites were flooded with people in Sydney's Bondi beach

On Wednesday, authorities reported that cases had also been detected on the other side of Sydney, some 65km (40 miles) away from known hotspots.

The outbreak was also causing concern in New Zealand, after an infected person travelled from Sydney to Wellington.

New Zealand authorities introduced a number of restrictions on Wednesday, while the "travel bubble" that allows people to fly between the two countries was closed to passengers from Sydney.

Lockdown fears

There is public speculation that Sydney may enter a lockdown if case numbers continue to increase.

Unlike other state capitals Melbourne and Brisbane, the city has tended not to enter snap lockdowns following outbreaks in the community.

The New South Wales state government has instead relied on swift and comprehensive contact-tracing systems and more localised lockdowns.

Australia's Covid case numbers have been relatively low compared to other developed nations. It has recorded 910 deaths and about 30,360 cases.

The country has relied on strict border controls, tough social-distancing rules and quick contact tracing to keep infection rates low.

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