Heathrow saw a 4.8% year-on-year decline in passenger numbers in February due to coronavirus.
The UK’s busiest airport said the fall to 5.4 million passengers was driven by lower demand on Asian and European routes.
The figure takes into account the extra day last month as 2020 is a leap year.
Heathrow warned that demand has continued to weaken in March.
The airport’s chief executive, John Holland-Kaye, said: “The threat of coronavirus is an increasing challenge for the UK and we are working day and night to ensure Britain’s front door is open and safe for our people and passengers.
“We will continue to work with the Government to limit the impacts this will have on UK plc.”
The impact of coronavirus on global trade is highlighted by the amount of cargo passing through Heathrow last month falling by 9.5% to 115,900 metric tonnes.
Airlines have cancelled thousands of flights due to the drop in demand for air travel.
British Airways – the largest airline at Heathrow – has stopped flying to mainland China and Italy while frequencies have been slashed on other routes.
It is possible to book a return flight from Heathrow to New York – departing on March 16 and coming back a week later – for £269, which after taxes, airport fees and “carrier charges” leaves a fare of just £1.
Low-cost carrier Norwegian announced on Tuesday that it has cancelled around 3,000 flights between mid-March and mid-June, which represents about 15% of its total capacity.
EasyJet and Ryanair have cancelled hundreds of flights while Virgin Atlantic has admitted some of its planes are “almost empty”.
The International Air Transport Association, which represents airlines around the world, has predicted that revenue losses for 2020 could reach 113 billion US dollars (£88 billion).