Doctors have warned the London Underground could be a hotbed for the spread of the highly-contagious coronavirus.
There have been nine confirmed coronavirus cases in the UK confirmed so far, as British hospitals brace themselves for more.
The Tube is used by an estimated 2 million people a day, and many more also use rail networks and buses in and around the bustling capital.
An estimated 9 million people live in London, but the city's population swells to more than 10 million on an average day - taking into account commuters into the capital for work, tourists and visitors.
The extensive transport network and huge population means tracking down potentially infected people is next to impossible to do with any urgency.
The warning for Tube riders comes after a London woman became the ninth person in the UK to test positive for the deadly virus.
There are concerns the city's status as a transport hub could exacerbate the spread of the virus, officially dubbed COVID-19 by the World Health Organisation this week.
German scientists this week warned coronaviruses, which included SARS and MERS, can linger on areas that are frequently touched, such as crowded Tube stations and hospital surfaces, for days.
The novel coronavirus is thought to be spread by air droplets, and Germany's Institute of Hygiene and Environmental Medicine at Greifswald University Hospital warned it could survive on surfaces such as bus and train poles and door handles for nine days.
However doctors have said the risk of infection for residents in the capital remains low.
"In general, if an initial case is in a densely populated area, then the risk of sustained person-to-person transmission following is higher," Dr Robin Thompson of Oxford University said.
"This is exacerbated by the fact that London is a transport hub, and the underground could provide a network to spread the virus quickly.
"As a result, given this case was in London, it might be expected that there is an increased risk posed by this case compared to the others we have seen."
Dr Michael Head from the University of Southampton added: "It should also be noted that of the 1,750 tests carried out so far in the UK, over 99% of those tested have been negative for the coronavirus.
"Thus, risks to Londoners and UK residents remain low, though people should continue to keep an eye on guidance for the general public."
While the patient has now been quarantined, Dr Thompson says the risk of the virus spreading depends on the woman's interactions prior to being placed in isolation.
"The key factor here is the number of contacts that this infected individual has had prior to being isolated," he said.
"If this is low, then the risk of sustained human-to-human transmission is also low."
As Public Health England investigates the patient's movements, Dr Nathalie MacDermott from the National Institute for Health Research said London commuters should continue to go about their business as usual.
"Provided the individual followed the government's advice (to self-isolate) there should be little concern of transmission to the general public in London," she said.
Brits quarantined at Arrowe Park Hospital, in the Wirral, after they travelled back from the virus' epicentre in the Chinese city of Wuhan, are set to released soon after testing negative for the sickness.
Meanwhile, the Government has ordered hospitals to create quarantine pods as a precaution at A&Es around the UK, as hospitals ready themselves to isolate new suspected cases.
Scientists around the globe are racing to create vaccines and drugs to stem the outbreak.
The death toll in China, where the virus originated, has risen sharply to at least 1,357, with the number of cases of the infection topping 60,000.
