An Air France flight bound for Detroit was diverted to Montreal after a passenger from the Congo boarded a flight in Paris "in error" amid flight restrictions tied to the Ebola outbreak, US Customs and Border Protection said.

A spokesperson for the agency on Thursday said the passenger "should not have boarded" the plane Wednesday due to US entry restrictions put in place to reduce the risk of Ebola spreading.

The spokesman said in an email officials "took decisive action and prohibited the flight carrying that traveller from landing at Detroit Metropolitan Wayne County Airport, and instead, diverted to Montreal, Canada".

Air France said the Congolese passenger was denied entry into the US due to new regulations that travellers from certain countries, including the Congo, can enter only through Washington.

The Department of Homeland Security also said that as of Thursday all US-bound American citizens and permanent residents who have been in Congo, Uganda or South Sudan in the previous 21 days must only enter through Washington Dulles International Airport for enhanced screening.

Craig Currie, spokesman for the Public Health Agency of Canada, said US officials informed Canadian authorities that the plane was refused entry due to their temporary travel restrictions for anyone who travelled to the Democratic Republic of Congo, Uganda, and South Sudan within the previous 21 days.

Currie said a public health official in Montreal assessed the traveller as asymptomatic. He said the traveller has flown back to Paris.

"Air France flight AFR378, along with all other passengers, continued to its original destination of Detroit," Currie said in an email.

The World Health Organisation on Sunday declared the Ebola outbreak a public health emergency of international concern. The outbreak is linked to the Bundibugyo virus, which is rarer than others and there is no available vaccine or medicine for it.