BEIJING—Public-health experts around the world have been crunching numbers about the advance of China’s dangerous new coronavirus to estimate how far and fast it could spread.

Studies published in recent days say the new virus appears to be more contagious than seasonal flu and on par with the similar pathogen behind an outbreak of severe acute respiratory syndrome in 2002 and 2003. The new virus’ mortality rate, however, is far below that of SARS.

China says that as of Sunday there were 5,142 infected people in Wuhan, the locked-down city where the outbreak began. Some scientists estimate based on statistical models that the number could be in the tens of thousands.

As health authorities race to control the outbreak, they are also scrambling to figure out, based on imperfect data, how the virus is transmitted, the length of the incubation period and the degree to which people without symptoms can spread the disease.

China’s health commission says incubation is generally between three and seven days, with the longest period being 14 days, and that people can spread the virus before appearing ill. That makes a two-week quarantine an important prevention measure—and casts doubt on the efficacy of temperature checks, the main screening method at immigration and other checkpoints.