WASHINGTON (Reuters) - Two planes with about 300 passengers, mostly U.S. citizens, took off from the Chinese city of Wuhan on Thursday bound for the United States -- the third group of evacuees from the heart of the coronavirus outbreak, the U.S. State Department said.

One of the flights had room to accommodate more than 60 Canadians, who will disembark on a stopover in Vancouver, British Columbia, before the remaining passengers continue on to the United States, a State Department spokeswoman told Reuters.

The plane stopping in Vancouver will fly on to Marine Corps Air Station Miramar in Southern California, the Pentagon said in a separate statement.

The second aircraft is headed for Omaha, Nebraska, by way of Lackland Air Force Base in San Antonio, Texas, following a refueling stop in California, the Defense Department said. Both planes are due to arrive on Friday.

The Defense Department has set aside surplus housing at each of those and a handful of other U.S. bases as quarantine sites for American evacuees arriving from Wuhan or the surrounding province of Hubei, where the coronavirus originated.

The first evacuation flight from Wuhan, carrying 195 State Department employees, their family members and other Americans, arrived Jan. 29 at March Air Reserve Base near Los Angeles.

Another group of nearly 350 Americans airlifted from Wuhan arrived on Wednesday aboard two cargo jets - 178 of them taken to Travis Air Force Base in northern California and 167 others to Miramar near San Diego.

Following the same procedures of previous flights, the latest wave of evacuees will be met by personnel from the Centers for Disease Control and Prevention (CDC) for screening and will be placed under quarantine for 14 days, the extent of the incubation period for the coronavirus, the Pentagon said.

Any who show signs of illness will likely be hospitalized in isolation off base, as have a total of at least six passengers who exhibited fever, cough or other possible symptoms of the disease upon their arrival at Travis and Miramar.

The United States and other countries have stepped up efforts to evacuate their citizens from China, where the coronavirus outbreak has infected more than 30,000 people and killed at least 600, most in and around Wuhan.

The CDC has said the risk of widespread transmission of the disease in the United States remains very low, but the Trump administration last week declared a U.S. public health emergency to ensure containment of the virus.

Twelve cases have been confirmed in the United States, none fatal. All but two of the patients were infected while traveling to China. Just two cases are known to have been transmitted person-to-person within the United States - both spouses of individuals who were infected abroad.

Starting this week, the U.S. government has barred U.S. entry of all foreign nationals who have recently been in China.

The CDC also has ordered mandatory two-week quarantine for all U.S. travelers who have visited China’s Hubei Province, while Americans who were elsewhere in mainland China are subject to 14 days of self-quarantine and monitoring.

All commercial flights carrying Americans home from China are being directed to one of 11 U.S. international airports, where passengers are screened by the CDC.