A federal judge in Florida has voided the national mask mandate covering airplanes and other public transportation as exceeding the authority of US health officials.

The decision on Monday by US District Judge Kathryn Kimball Mizelle, in Tampa, also said the Centres for Disease Control and Prevention improperly failed to justify its decision and did not follow proper rulemaking.

The CDC recently extended the mask mandate, which was set to expire on April 18, until May 3 to allow more time to study the BA.2 Omicron subvariant of the coronavirus that is now responsible for the vast majority of cases in the US.

The mask requirement for travellers was the target of months of lobbying from the airlines, which sought to kill it.

The carriers argued that effective air filters on modern planes make transmission of the virus during a flight highly unlikely. Republicans in Congress also fought to kill the mandate.

Critics have seized on the fact that states have rolled back rules requiring masks in restaurants, stores and other indoor settings, and yet Covid-19 cases have fallen sharply since the Omicron variant peaked in mid-January.