And in one of the most dramatic measures, the tiny Pacific nation of Papua New Guinea announced Wednesday that travellers from Asia would not be allowed in.
The Department of Health and Social Care said on Tuesday that 97 people in the United Kingdom had been given the all-clear for the virus, although scientists say it may have already entered the country.
China has cut off access to Wuhan and 16 other cities in Hubei province to prevent people from leaving and spreading the virus further.
The boy's family flew from their home in Shenzhen, a city in the south of the country next to Hong Kong, to Wuhan on December 29 to visit relatives, including one who was in a hospital.
The Boeing 747 aircraft stopped at Ted Stevens Anchorage International Airport in Anchorage, Alaska on Tuesday to refuel.
Before they headed to California, the 201 passengers onboard had already undergone four health screenings: two in Wuhan before their flight took off, and two after they arrived in Anchorage.
Dubbing themselves "construction site supervisors", as many as 25 million Chinese netizens at a time have been closely monitoring the building of the hospitals, known as Leishanshan and Huoshenshan, on an around-the-clock, live broadcast by China Central Television.
Hundreds of Brits returning to the United Kingdom from the centre of the coronavirus crisis will be placed in quarantine for two weeks to stop the infection spreading.
The source of the virus and the full extent of its spread are still unknown.
From France to Japan, governments were organising evacuations, while Hong Kong - a scene of anti-China unrest for months - planned to suspend rail and ferry links with the mainland.
The World Health Organization (WHO) has said it is confident in China's ability to contain the coronavirus, but concerns are mounting as its health authorities said the number of confirmed cases had jumped by 1,459 to 5,974.
Bichat Hospital is leading French efforts to treat patients with the virus, but hospital officials said it only has nine beds for infected patients. Vietnam is investigating another case. He also declined to say how many people Emirati health authorities had contacted while tracing the family's travel in the UAE.
The man's case is still considered a presumptive positive pending confirmation from a laboratory in Winnipeg, but Dr. Henry said "we are confident this is truly a case of this novel coronavirus".
Washington had offered China assistance three times so far without success, Health and Human Services Secretary Alex Azar told reporters.
The virus is weighing heavily on the world's second-biggest economy.
Japanese automaker Toyota said Wednesday it would keep its plants in China closed until at least February 9 in part due to government guidelines.
Global coffee chain Starbucks said it expected a significant earnings hit after closing more than half of its stores across China.