Hong Kong's airport said Friday that some airlines had been affected by an IT outage, as widespread technical problems were reported by flight operators around the world.

"A Microsoft outage that has disrupted the service of airlines worldwide is affecting some of the airlines at Hong Kong International Airport," the Airport Authority said in a statement.

"Flight operations at (Hong Kong's airport) have not been affected."

At the airport, crowds of people waited in long lines, while staff members carried handwritten signs to direct passengers to different check-in counters.

A 38-year-old woman surnamed Wong told AFP that she and her family waited in line for around an hour to be checked-in for their HK Express flight to Chiang Mai.

She said staff had written down their boarding information by hand and the process "felt chaotic".

Hong Kong's flag carrier Cathay Pacific told AFP that self-service check-in facilities had resumed after experiencing "unexpected issues with our technical providers".

Facial recognition at bag drop facilities "as well as flight booking/redemption services via our website, remain temporarily unavailable", it said in a statement.

Cathay's subsidiary HK Express said self-service check-in facilities and departure control systems had been affected.

"Due to a global service outage of Microsoft, Navitaire, our global e-commerce system has been affected," the airline said on its official Facebook page.

HK Express said it had reverted to manual check-in processes after its website and mobile apps were affected.