Canadians trapped in the coronavirus-affected region in Wuhan, China could be permitted to leave starting Thursday — but not everyone who registered for the airlift is guaranteed a seat on the first flight out, according to Canadian officials.

The chartered aircraft, which seats 250 people, is now on its way to Hanoi, Vietnam where it will be on standby to make its way to Wuhan, China.

Global Affairs Canada sent an email to Canadians in the region overnight saying a government-chartered flight is expected to leave Wuhan Tianhe International Airport in the early morning of Feb. 6.

"Due to demand and the restrictions associated with this flight, we cannot guarantee that everyone who is eligible for a seat will be able to board the plane," says the email, a copy of which was obtained by CBC.

"You should make plans for the eventuality that you are not able to board the plane."

A government official cautioned that a departure time has not been confirmed because Canada is still awaiting final approvals for entering restricted airspace from the Chinese government.

The plane we have chartered to assist those Canadians in <a href="https://twitter.com/hashtag/Wuhan?src=hash&ref_src=twsrc%5Etfw">#Wuhan</a> and <a href="https://twitter.com/hashtag/HubeiProvince?src=hash&ref_src=twsrc%5Etfw">#HubeiProvince</a> who wish to leave is currently on its way to <a href="https://twitter.com/hashtag/Hanoi?src=hash&ref_src=twsrc%5Etfw">#Hanoi</a> in Vietnam where it will be prepositioned for departure to China when final approvals are granted. <a href="https://t.co/EehBS2LYeH">pic.twitter.com/EehBS2LYeH</a> —@FP_Champagne

The number of cases of the new coronavirus has climbed to more than 20,000 worldwide, with more than 400 deaths. There have been five cases in Canada to date — three in Ontario and two in British Columbia.

The second reported case of coronavirus in B.C. — a woman in her 50s who became ill a few days ago — was confirmed through testing last night and announced by the province's health officer on Tuesday.

Foreign Affairs Minister François-Philippe Champagne announced on Twitter Tuesday that the plane had left for Hanoi and will carry on to China when final approvals are granted.

Champagne said the numbers have been fluctuating, but there are now about 300 Canadians requesting repatriation. Based on past evacuations, about 20 per cent of those individuals could be "no shows" who choose not to leave for various reasons, he said.

WATCH | Foreign Affairs Minister François-Philippe Champagne on Wuhan airlift:

Foreign Affairs Minister Francois-Philippe Champagne spoke to reporters after the weekly Cabinet meeting 2:56

China's policy is to only allow foreign nationals travelling on foreign passports to leave the country, as a measure to prevent the spread of the virus. China made an exception to allow permanent residents of Canada and Chinese citizens to leave if they're accompanying a child who is a Canadian citizen.

Champagne acknowledged that could mean some families could be split up.

"We have been advocating for repatriation because obviously I saw on the news the families' stories. Everyone wants to do their best to bring all these people home. I understand their attachment to Canada. They want to come back and I feel the compassion to bring them," he said.

"However, I have to work with the Chinese health authorities who have been very clear that those who will be allowed to board are foreign nationals travelling on foreign passports."

WATCH | Prime Minister Justin Trudeau on Wuhan evacuation:

Prime Minister Justin Trudeau stops to answer questions about the government's plans to evacuate Canadians and others from Wuhan, China. 0:44

Prime Minister Justin Trudeau said that more people have asked to be on the evacuation flight than the aircraft can carry.

"That's why we have already got an option on the second plane," he said before a cabinet meeting Tuesday. "Though we've already seen the experience of the countries that sometimes people who want to come aren't able to make it to the airport. So we'll make a decision based on how full the plane is when we come back, whether or not we exercise the option of the second plane."

China 'fully co-operative'

The opposition Conservatives have suggested there has been a delay in the airlift operation due to strained diplomatic relations between Canada and China. Trudeau rejected that claim Tuesday.

"China is being fully co-operative with Canada. There's just a lot of processes to make sure they can get through the local quarantines on their way to the airport, that all the proper paperwork is filled out, that identities are verified and triple-verified," he said.

Heather Jeffrey, a senior official with Global Affairs Canada, told a committee of MPs studying Canada-China relations that the evacuation has "unique challenges," including overflight clearance and visa requirements.

Jeffrey said Canada extends consular services to Canadian citizens and permanent residents in cases of natural disaster or humanitarian situations. In the case of Wuhan, the Chinese government has been firm on allowing only foreigners to leave, and has made exceptions so far only for permanent residents who need to accompany minors who are Canadian citizens.

"We recognize it is an extremely difficult situation to be confined and to not have an opportunity for departure," she said.

Jeffrey said there are now 565 Canadians registered in the Hubei province of China, where cities like Wuhan and others are now under lockdown.

WATCH | Health Minister Patty Hajdu on evacuation plan:

Health Minister Patty Hajdu spoke to reporters after the weekly Cabinet meeting 0:32

Health Minister Patty Hajdu said officials have carried out a "run-through" of procedures for the evacuation.

"We are ready for whenever the plane arrives," she said Tuesday.

The airlift also also will carry medical supplies, such as masks and medical protective clothing, for delivery to Wuhan to assist Chinese authorities.

Hajdu said travellers showing symptoms of coronavirus or other respiratory illnesses will not be allowed to board the Canadian plane as a precaution, and there will be various levels of screening and monitoring throughout the process. If anyone develops symptoms during the flight, they will be separated from others on board.

Each person will only be allowed to bring one carry-on bag.

Once back in Canada, the evacuees will be transported to Trenton air base, where they must remain under quarantine for 14 days.

Federal officials are now on the ground in Wuhan to co-ordinate the airlift. All staff taking part in the airlift will be wearing protective gear.

Hajdu said if a second plane is needed, the process likely will be much swifter than it was for the the first aircraft. At the earlier stages of the outbreak, there were relatively few Canadians who had registered as being in the region and the government thought they could be extricated using allied partners.

"We weren't actually thinking we had the demand that we did, and once it became clear in the next couple of days of speaking about the need to register with Global Affairs Canada, it became clear that we were going to need our own plane," she said.

Quarantine in Trenton, Ont.

The federal government will absorb the costs of the airlift and the passenger quarantine.

"This is what Canadians do. We help each other," Hajdu said Monday. "We've got 300 Canadians stuck in a quarantined city where life is becoming incredibly difficult, if not almost impossible, in some situations."

WATCH | What we know about the new coronavirus so far:

Information about the coronavirus outbreak is spreading fast, but what do we actually know about the illness? CBC News medical contributor and family physician Dr. Peter Lin breaks down the facts about what it is, where it came from, how it spreads and what you can do to protect yourself. 5:10

Canada's Chief Public Health Officer Dr. Theresa Tam said developing a vaccine could take up to a year. For now, she said, the best way to prevent the spread of the virus is to restrict its transmission.

The World Health Organization has declared the coronavirus outbreak a global health emergency, but has praised China for its efforts to contain the virus.