China's move to lock down 10 cities to control the spread of a new coronavirus is unprecedented in modern history and its effectiveness is hard to predict, public health experts say.

In Wuhan, the epicentre of the outbreak, the train station and airport were shut down on Thursday, while ferry, subway and bus service ground to a halt.

Trying to contain a city of 11 million people is "new to science," said Gauden Galea, the World Health Organization's representative in China. "We cannot at this stage say it will or it will not work."

Similar measures were announced in other cities, all in central China's Hubei province.

Mass gatherings were forbidden just as hundreds of millions of people prepared to travel and celebrate the Lunar New Year.

"That's just incredible," said Dr. Isaac Bogoch, an infectious disease physician at Toronto General Hospital. "The equivalent would be shutting down transportation to a comparable sized city like London, United Kingdom on Dec. 23."

But its effectiveness depends in part on how many "chains of transmission" have occurred.

Like branches of a tree trunk, each chain of infection represents one person infecting someone else. Many chains of infection usually means more people are infected and an outbreak is widespread, he said.

If there have already been secondary chains outside Wuhan, then shutting down the transportation might slow the spread of the virus, but not stop it in its tracks.

Bioethicist Kerry Bowman of the University of Toronto says quarantines can be effective in the early stages of an outbreak.

The rub is, in this case, the quarantine pits individual freedoms against an entire city's.

"This may be acceptable to people if it's short term," Bowman said.

For China, the question becomes who does the quarantine serve, says Ann Carmichael, a professor emerita of history at Indiana University who studies quarantines during the 17th century outbreaks of plague in Europe.

Passengers arrive at Sydney International Airport in Australia on Thursday. Quarantines can restrict the movement of citizens. (Don Arnold/Getty Images)

Back then, she says, people would be killed for the tiniest infraction of public health laws, like not burning clothing as ordered. The word "quarantine" comes from the Italian quaranta giorni ("40 days"), which referred to a period of isolation placed on ships and people in a bid to control the Black Death.

These days, says Carmichael, "I think what the Chinese government is always thinking about is — when does panic make it worse, and what is a measured response?" she said.

Panic is a possible side-effect of a quarantine, says Dr. Tom Solomon, who heads the U.K.'s Health Protection Research Unit on emerging infections. He says stopping all public transport from a city can be counterproductive.

Skeletons suspected to have come from a cemetery for victims of the bubonic plague that ravaged Europe in the 14th century shown in London in 2014. The Black Death, as the plague was called, is thought to have killed at least 75 million people in the 1300s, including more than half of Britain's population. (Lefteris Pitarakis/The Associated Press)

"It can increase the level of panic and just cause people to flee by other means," Solomon wrote in a recent commentary.

It can also send people into hiding. Solomon gave the example of the village of Eyam in north England where, in the Middle Ages, residents built a wall during an outbreak of plague and didn't leave until it ended.

Back then, outbreaks of plague, cholera and yellow fever provided a reason for one country to interfere in another's affairs. It wasn't until the 19th century that countries began to co-operate more officially on global health problems.

And today, says Carmichael, the world needs answers to questions — like whether this new coronavirus is poised to cause a pandemic, like the 1918 influenza.

Toronto General Hospital employee Maria Tanta, left, a recovery room nurse, had her temperature checked by Callie Dunne, an nurse in Occupational Health and Safety in April 2003. (J.P. Moczulski/Canadian Press)

More recent infections prompted a range of responses. During HIV/AIDS, the World Health Organization did not get involved in quarantines or border restrictions, Carmichael said.

During the SARS outbreak in Ontario, hospitals and long-term care homes practised a form of quarantine — with daily temperature checks for staff and a ban on visitors.

In contrast, after SARS, Canada helped to revise International Health Regulations to avoid unnecessary restrictions on travel and trade.

Carmichael said part of the history and practice of quarantine is "keeping in" — detention, confinement and isolation. The other is "keeping out" — border security, masks on persons and aggressive hand washing.

Health officials in Canada and the U.S. continue to emphasize hand hygiene.