The closure resulted in delays to about 60 per cent of flights, or 186, between 7am and 3pm. The Airport Authority said failure of the plane's hydraulic system resulted in a lengthy maintenance operation.
"Due to the hydraulic system breakdown, the time needed to handle the emergency at the runway took longer than expected," an authority spokesman said.
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The authority reopened the north runway at 3.45pm. It is Hong Kong International Airport's third runway and has been in operation since 2022.
The authority, which operates the airport, said the incident took place at around 7.30am. That left the south runway as the only one operating, with the airport's second one closed for modification works.
It was not immediately clear why the aircraft, a Boeing 747 freighter, made an emergency return.According to data available online, the cargo flight was Atlas Air 5Y4304.
The aircraft departed at 4.09am for Anchorage in the United States before making a U-turn near Taipei an hour later and arriving back in Hong Kong.
The aircraft was earlier surrounded by several service vehicles. Goods were also unloaded from it.
