BEIJING — The Chinese authorities on Sunday said that 17 more people had been infected with a mysterious new virus, adding to concerns about the spread of the illness ahead of China’s busiest travel season.
The health commission in Wuhan, a central city, said in a statement that the infected people began showing symptoms of the pneumonialike coronavirus as recently as last week. Three are now in critical condition, the commission said.
The new cases suggest that the illness, which has killed two people and sickened at least 62 in China, is continuing to spread. Public health officials are working to stop a major outbreak of the virus ahead of the Lunar New Year holiday, when hundreds of millions of people in China are expected to travel. The holiday begins Friday.
Already, the virus appears to have spread outside China’s borders. Officials in Thailand and Japan have confirmed three cases involving people who have traveled through Wuhan.
The authorities said that most people with the infection had contracted it through exposure to animals at a market in Wuhan that sells seafood and live animals, and it was uncertain whether the virus could spread from human to human.
But the health commission in Wuhan also acknowledged on Sunday that some people who had come down with the virus had no exposure to the market.
That acknowledgment could suggest that the virus could be present in other markets in Wuhan, experts said, raising concerns that more people might be at risk.
“If you cannot find the source and control the source of the virus, you cannot extinguish the fire,” said David Hui, the director of the Stanley Ho Center for Emerging Infectious Diseases at the Chinese University of Hong Kong.
Dr. Hui said the risk of human-to-human transmission still appeared to be low, though he noted that the virus could mutate.
Some experts have suggested that there are most likely far more cases of the illness than the authorities have disclosed. In previous incidents, including during the 2003 outbreak of severe acute respiratory syndrome, or SARS, the Chinese government has withheld critical information, drawing widespread criticism.
One estimate on Friday by the MRC Centre for Global Infectious Disease Analysis at Imperial College London suggested that there could be as many as 1,700 cases.
The new virus has brought back memories in China of the SARS outbreak, which was also caused by a coronavirus. That virus, which is believed to have jumped to humans from animals at markets, originated in China and was spread to other countries by travelers, infecting more than 8,000 people and killing more than 800.
While the new coronavirus so far seems to be less severe than SARS, public health officials around the world are exercising caution.
On Friday, the Centers for Disease Control and Prevention in the United States announced that airports in New York, San Francisco and Los Angeles would begin screening passengers from Wuhan for the virus.
Elsie Chen contributed research.