To get permission to leave China's coronavirus epicenter and return to his job in Hong Kong, a Chinese banker needed two things: a letter from his company and a green health code from an Alibaba app.

The man, who gave his name only as Clarence because of privacy concerns, secured the necessary permission last week and boarded a high-speed train to the border city of Shenzhen.

"It was like the drama 'Prison Break.' There are so many levels to go through and so many barriers to overcome," he said of the challenges of leaving Hubei province.