WUHAN, China — The authorities drastically expanded a travel lockdown in central China on Thursday, essentially penning in more than 35 million residents to contain a deadly virus that is overwhelming hospitals and fueling fears of a pandemic.

The new limits — abruptly decreed ahead of the Lunar New Year holiday, China’s busiest travel season — were an extraordinary step that underscored the ruling Communist Party’s deepening fears about the outbreak of a little understood coronavirus. It has killed at least 26 people and sickened more than 800 in China and at least six other countries, including the United States, according to statistics from health officials.

In Wuhan, the Hubei provincial capital of 11 million where the outbreak began, anxiety and anger prevailed as worried residents crowded into hospitals and teams of medical workers in hazmat suits sought to identify the infected.

“They can’t take proper care of all the people here,” said Sun Ansheng, a man in his 50s who was waiting outside a hospital while his wife was tested for the coronavirus, so named because of the spiky halo around the microorganism.