Hong Kong International Airport (HKIA) has again suspended all passenger flights due to ongoing protests just hours after re-starting operations.

The world's busiest freight hub began allowing flights to take-off earlier today after a suspension was put in place yesterday due to hundreds of protesters occupying the main arrivals hall.

However, just a couple of hours ago the airport authority issued an update saying flights had once again been stopped.

Freighter flights are unaffected by the disruption.

"Terminal operations at Hong Kong International Airport have been seriously disrupted, and all check-in processes have now been suspended. All passengers are advised to leave the terminal buildings as soon as possible. Affected passengers please contact their respective airlines for flight arrangement," HKIA said.

Home carrier Cathay Pacific added: "Cathay Pacific and Cathay Dragon have been informed by the Airport Authority in Hong Kong that all check-in has been suspended as a result of the public assembly at Hong Kong International Airport, which is ongoing. There is potential for further flight disruptions at short notice.

"Customers are therefore encouraged to postpone non-essential travel from Hong Kong on Tuesday 13 August and Wednesday 14 August and should not proceed to the airport.

"While disruption events like these can change significantly and at short notice, rest assured we are doing everything we can in advance to minimise the impact to our customers."

During the past five days, thousands of protesters have gathered inside the terminal, causing serious disruption to the airport’s flights and operations.

The protests in Hong Kong, catalysed by a controversial extradition bill, have been ongoing for two months.

The airport disruption is not the only challenge faced by Cathay Pacific as a result of the protests.

Last week, the Civil Aviation Administration of China (CAAC) placed a series of conditions on Cathay Pacific on safety grounds after members of its staff were found to be taking part in the protests.