The top shareholder and manager of Cathay Pacific Airways has condemned protests in Hong Kong and vowed to follow China's aviation rules after the airline suspended a second pilot as deepening unrest hit its operation and stock.

Cathay, whose strong British links make it a symbol of Hong Kong's colonial past, has emerged as the highest-profile corporate target as Beijing looks to quell protests in the territory that have gone on for ten straight weeks.

Shares in the Hong Kong flag carrier sunk to a 10-year low, hit by concerns that Beijing could slap further sanctions on the airline, causing more damage to its brand.

Just last week, China's aviation regulator demanded Cathay suspend personnel who engaged in or supported illegal protests in Hong Kong from staffing flights into its airspace, a directive the carrier complied with by suspending a pilot.

The airline also fired two ground staff and sent out a warning email to its employees.

"We condemn all illegal activities and violent behaviour, which seriously undermine the fundamental principle of 'One Country, Two Systems' as enshrined in the Basic Law," Swire Pacific Ltd said in a statement.

Cathay's manager said it supported the Hong Kong government, CEO and police in their efforts to restore law and order.

Demonstrators say they are fighting the erosion of the "one country, two systems" arrangement enshrining some autonomy for Hong Kong when China took it back from Britain in 1997.

Swire Pacific's comments supporting Beijing come a day after China's aviation regulator said its deputy director had met with Swire Pacific Chairman Merlin Swire.

Cathay, which was forced to cancel hundreds of flights after Hong Kong's airport authority took an unprecedented step of closing the airport on Monday, has warned of further flight disruptions at short notice.

Cathay suspended a second pilot on Tuesday, reportedly for encouraging protesters to keep protesting at the Hong Kong airport. Cathay said the action was taken over "misuse of company information" and declined to comment further.

Analysts and employees said there were fears that Beijing could take further action that could hit the airline, such as time-consuming plane checks at airports or even the closure of Chinese airspace and airports to Cathay flights.

Some Cathay employees expressed concerns over what the firm's position could mean for them. "I think there is an underlying concern now about what this does to Cathay," one of the airline's pilots said of the regulatory scrutiny.

"This could be a storm in a teacup and we'll be back to making lots of money next month. Or this could be the collapse of the airline. No one really knows," the pilot told Reuters.