The ground-zero of the new coronavirus, Wuhan, is cautiously reopening after a two-month quarantine, but the birthplace of the global coronavirus pandemic is now on guard against a potential new threat: imported cases.

Wuhan, at the peak of the crisis, recorded thousands of fresh cases daily. That has dropped to zero. But with the U.S., Europe and other regions now struggling with their own outbreaks, China is reporting dozens of imported cases each day and has shifted the focus of its prevention effort to the external threat.

Travel restrictions have been loosened, with Wuhan's busy train station officially resuming inbound services on Saturday and highways reopened as the unprecedented lockdown that kept more than 50 million people across Hubei province housebound is lifted. That has unleashed a reverse tide of local residents who were stranded elsewhere in China, where many reported facing ostracism or restrictions on their movements, and are now flocking back to homes they have not seen for at least 10 weeks. The returnees, many arriving by train wearing two face masks, latex gloves and protective suits, bring with them the potential for a new round of infections, and authorities are taking few chances.

Before leaving Wuhan's station, all passengers are required to register their personal details and travel history before proceeding through temperature checks. They also must show either a certificate of good health or a "green" rating, for "safe," on a mobile phone app system that has been adopted nationwide and uses big data to track whether a person visited any high-risk areas in China. Without that, travelers must submit to a nucleic acid test for the virus, an official in Wuhan's Jiangan district told AFP. Those who report or who are suspected of having traveled abroad recently are sent to a separate registration area, where workers in hazmat suits check their details.

The rising number of imported coronavirus cases in China has raised the possibility that the country will undergo a second wave of infections, a spokesman of the country's health authority said on Sunday. "China already has an accumulated total of 693 cases entering from overseas, which means the possibility of a new round of infections remains relatively big," said Mi Feng of the National Health Commission. China reported 45 new cases of coronavirus Saturday, all but one of which were patients diagnosed after entering the country from overseas.