WUHAN, China—The city in central China where a new coronavirus originated will halt outbound flights and trains and shut its public-transportation system, the Chinese government said, a dramatic escalation in the battle to contain a pneumonia outbreak that has killed at least 17 people.

The decision to lock down Wuhan, a major travel hub and a city of 11 million, comes as the country is entering one of its busiest travel periods, its Lunar New Year holiday. Hundreds of millions will travel across China and outside the country, increasing the risk of transmission for the virus.

After days in which authorities appeared reluctant to impose sweeping bans on the movement of the general public in Wuhan, the mood began to shift on Monday, when the number of confirmed cases jumped and health authorities confirmed the virus could be transmitted between humans.

That day, President Xi Jinping gave his first public direction to officials to work with international authorities and share information more openly. Since then, as the number of deaths and confirmed cases has risen, authorities in Wuhan have stepped up their own countermeasures.

The lockdown will begin at 10 a.m. local time on Thursday and continue for an indefinite period, Wuhan health authorities said. Service on subways, city buses, long-distance coaches and ferries will also be suspended.