MELBOURNE, Australia — The city that was once Australia’s worst COVID-19 hot spot increased pandemic restrictions Tuesday after identifying a cluster from someone infected in quarantine.

Masks became mandatory indoors in Melbourne, home gatherings were restricted to five visitors and outdoor gatherings were limited to 30, Victoria state’s Acting Premier James Merlino said. The restrictions will apply until June 4.

New Zealand was halting quarantine-free travel to Victoria for three days from Tuesday evening. Health officials said they were taking a cautious approach as there were several unknowns about the Melbourne outbreak.

The cases are linked to a Melbourne traveler who became infected in hotel quarantine in South Australia state earlier this month. Five cases were confirmed Tuesday by Victoria state’s Health Department, bringing the cluster to nine since Monday.

Australia’s second-largest city had an outbreak last year that peaked at 725 new cases in a single August day at a time when community spread had been virtually eliminated elsewhere in Australia. Victoria state, where Melbourne is the capital, accounts for 820 of Australia’s 910 coronavirus deaths.

New Zealand and Australia opened a quarantine-free travel bubble last month. Australian Prime Minister Scott Morrison is due to visit New Zealand on Sunday for the first time since the pandemic began.