A quarantine-free travel corridor between Australia and New Zealand that had allowed mutual visits between the countries freely amid the coronavirus pandemic was suspended Saturday night following a surge in cases in the major Australian city Sydney.

The government of Prime Minister Scott Morrison had aimed to launch a similar "travel bubble" arrangement with Singapore by the end of the year and possibly extend it to other countries, including Japan, but the latest development may complicate the plan.

Passengers wearing face masks hug as they walk to board their flight bound for New Zealand at Sydney"s Kingsford Smith Airport on April 19, 2021 in Sydney, Australia.(Getty/Kyodo)

Singapore and Hong Kong were planning to launch a travel bubble with each other but have been forced to postpone it repeatedly as local infections increased.

Travel bubble arrangements are conceived between countries and territories that have seen relatively low infections. Australia and New Zealand launched the two-way quarantine-free travel corridor in April.

The latest outbreak in Sydney, traced to a limousine driver who had transported international flight crew, has grown to over 100 confirmed cases as of Sunday. He had contracted the highly contagious Delta variant, first detected in India.

The New South Wales state government said Saturday it has extended the ongoing lockdown in central Sydney and other parts of the city until July 9, and including surrounding communities.

New Zealand on Wednesday stopped extending the travel bubble to passengers on flights into and out of Sydney. On Saturday, the minister in charge of the country's COVID-19 response, Chris Hipkins, announced a pause to the trans-Tasman travel bubble until Tuesday.

"Since the pandemic has started, this is perhaps the scariest period that New South Wales is going through," state Premier Gladys Berejiklian said Thursday in a warning to state residents.

Nonetheless, Australian cases are relatively few in terms of numbers per capita. According to the University of Oxford's Our World in Data project, Australia has cumulatively had about 1,200 infections per million people, compared with about 100,000 in the United States and about 70,000 in Britain and about 6,300 in Japan. New Zealand only has had about 570 cases per million.

The low numbers for Australia and New Zealand are the results of thorough border controls enforced by their governments. The two countries have barred the entry of foreigners in principle, effectively closing their borders. Their nationals are also required to undergo a two-week quarantine upon their return from other countries.