WASHINGTON (BLOOMBERG) - The US Centres for Disease Control and Prevention has issued a "strong recommendation" for mask-wearing by both passengers and operators on planes, trains, buses and taxis to prevent the spread of the novel coronavirus.

Masks should cover a person's nose and mouth and be worn while travelling in and out of the US as well as within the country, the agency said. Operators should require them for the entire time of travel and deny entry to anyone not wearing one.

"Travelling on public conveyances increases a person's risk of getting and spreading Covid-19 by bringing persons in close contact with others, often for prolonged periods, and exposing them to frequently touched surfaces," the guidance on the CDC website states.

It notes that many states, localities and other countries have implemented mask requirements, as have transportation operators.

The change was reported earlier by the Washington Post, which said it followed airline industry pressure and a request from Vice-President Mike Pence. A note at the bottom of the web page states it was last reviewed on Monday.

The new CDC guidance comes as travellers have begun flying anew, though still at far reduced levels compared with the year earlier. The airlines began requiring masks more than five months ago, and toughened their rules as the pandemic worsened across the US.

In June, Airlines for America, a trade group representing big carriers, said its members would step up enforcement of face coverings. The trade group has also encouraged federal officials and US airports to require masks.

There are only some select instances in which operators can allow masks to be removed, including briefly while eating and to verify one's identity during a security screening, according to the CDC.

Some exceptions to mask-wearing may occur, including for children under age 2, the agency said. CDC guidance has previously stated that travellers may wear masks, along with taking other safety measures like social distancing.