Hong Kong's leader on Thursday defended her policy of temporarily banning flight routes that bring in coronavirus cases, as a leading airline industry figure warned the city had fallen "off the map" as an aviation hub.

The city's airport was previously one of the world's busiest but has been largely cut off throughout the pandemic as Hong Kong hews to China's strict zero-Covid policy.

"Circuit breaker" rules mean any airline that brings in three or more infected passengers on a single flight is suspended from flying that route for seven days.

City leader Carrie Lam defended the policy on Thursday, saying flights were bringing in infections "probably because of the very relaxed approach adopted in many places" around the world.

Authorities have given some ground, lifting a complete flight ban on nine countries earlier this month following growing anger from the business community and Hong Kongers stranded overseas.

Lam said more than 1,000 residents have returned to Hong Kong daily this month, compared to just 200 a day previously.

"It is not right to say that this travel easing has no impact," she said.

Her comments came as the director general of the International Air Transport Association, Willie Walsh, warned Hong Kong was "effectively off the map".

"(Hong Kong) is going to lag significantly behind the recovery that we're seeing elsewhere," Walsh told reporters on Wednesday in quotes carried by Bloomberg News and the South China Morning Post.

Temporary flight bans have been frequently invoked, throwing travel plans into chaos as residents scramble to book new routes and change mandatory hotel quarantine bookings.

Six airlines including Emirates and Cathay Pacific have had routes banned this week.

Emirates' Dubai-Bangkok-Hong Kong route has been suspended six times for a total of 77 days this year, according to Bloomberg.

Walsh said Hong Kong's restrictions have been "very severe and have led directly to the cancellation of a lot of services, with airlines effectively finding it incredibly difficult, if not impossible, to operate there".

Last month 11 airlines and logistics giants sent a letter to the government calling for the removal of Covid-19 testing requirements for flight crews before take-off and on arrival.

Prior to the pandemic, Hong Kong's airport hosted about 200,000 passengers a day.

But the finance hub -- which dubs itself "Asia's World City" -- is now one of the world's most isolated places.

Lam's administration says there can be no change from zero-Covid even though the controls proved largely ineffective this year when the Omicron variant tore through.

Hong Kong has since recorded one of the world's highest mortality rates from the virus.