SYDNEY — Sydney's coronavirus outbreak grew to around 70 on Sunday, forcing authorities to introduce stricter social distancing rules across the city and more states to close borders or impose quarantine measures on its residents.

The neighboring state of Victoria will close its border to Sydney from midnight Sunday. South Australia state introduced a 14-day quarantine for all Sydney arrivals on Sunday and banned travelers from the affected suburbs.

The island state of Tasmania took a similar step on Saturday, while Western Australia state imposed a hard border closure. About a quarter of a million people in Sydney's northern beach suburbs, where the outbreak has occurred, have been put into a strict lockdown until Christmas Eve.

Tens of millions of people are expected to travel to family gatherings or winter vacations over Christmas, despite pleas by public health experts who fear the result could be another surge in Covid-19 cases.

In the U.S., AAA predicts that about 85 million people will travel between Dec. 23 and Jan. 3, most of them by car. If true, that would be a drop of nearly one-third from a year ago, but still a massive movement of people in the middle of a pandemic.

Jordan Ford, 24, who was laid off as a guest-relations worker at Disneyland in March, said he plans to visit both his and his boyfriend’s families in Virginia and Arkansas over Christmas.

“It is pretty safe — everyone is wearing a mask, they clean the cabin thoroughly,” said Ford, who has traveled almost weekly in recent months from his home in Anaheim, California, and gets tested frequently. “After you get over that first trip since the pandemic started, I think you’ll feel comfortable no matter what.”

Experts worry that Christmas and New Year’s will turn into super-spreader events because many people are letting down their guard — either out of pandemic fatigue or the hopeful news that vaccines are starting to be distributed.

“Early on in the pandemic, people didn’t travel because they didn’t know what was to come,” said Dr. Peter Chin-Hong, an infectious-disease expert at the University of California, San Francisco, “but there is a feeling now that, ‘If I get it, it will be mild, it’s like a cold.’”