The China television report showed Mr. Xi speaking to the six other members of the Politburo Standing Committee, the Communist Party’s topmost decision-making body, and a circle of other grave-faced officials. The leadership meeting took place on the first full day of China’s weeklong Lunar New Year holiday, a time when the entire country, including party leaders, usually take time off for family get-togethers and relaxation.

“Confronted with the grave situation of this accelerating spread of pneumonia from infections with the novel coronavirus, we must step up the centralized and united leadership under the party central” leadership, Mr. Xi said.

The Communist Party will establish a top-level team, called a leadership small group, to grapple with the crisis, the meeting said, giving efforts to fight the outbreak greater urgency and centralized coordination. Here are some of the other measures and main points announced:

Mr. Xi demanded strong efforts to provide medicine and other supplies, a point of anger among many doctors and medical workers in Wuhan who have complained about a shortage of protective masks, gowns and other safety equipment.

Officials in Hubei Province, where the outbreak began, received an implicit telling off. Residents and many other Chinese people have said that officials did not respond seriously enough. Hubei, the meeting said, “must make containment and control of the epidemic its topmost priority, adopting even stricter measures to prevent it expanding within and spreading outward.”

The meeting called for concentrating resources, experts and treatment to cope with the surge of infections, including sending patients with serious symptoms to designated medical units. This suggests that there may be more hospitals built or modified to deal solely with the outbreak.

Local and military medical resources are to be pooled for the response.

Public spaces across China, including railway stations, airports, and ports, were told to step up measures to deter the spread of the virus, including ventilation, disinfection, and body temperature checks for people. “When suspected cases are found they must be held for observation locally,” the meeting ordered.

In his remarks on Saturday, Mr. Xi also seemed to address Chinese citizens’ growing dissatisfaction with the official response. On Chinese social media, users have asked whether the authorities have accurately reported the number of cases or taken enough steps to rein in their spread.

Commenters have especially condemned the perceived absence of the local, provincial and even national authorities in the heart of the outbreak. Mr. Xi had made few public remarks about the disease before Saturday, when he called for officials to “stand at the front line to safeguard social stability.”

“Where is that person? He is not on the front line,” one user wrote on Weibo, a Twitterlike platform, an apparent reference to Mr. Xi. The posts were quickly deleted.

A professor of infectious diseases in Hong Kong who helped identify SARS, Guan Yi, has accused Chinese authorities of delaying action and of obstructing his efforts to investigate the outbreak.

Local officials in China have long had incentives to avoid revealing problems that might invite the wrath of party bosses. But Mr. Xi’s efforts to centralize power in Beijing have further weakened local authorities and increased their incentive to deny problems.