A major obstacle to the proposed new third runway at Chek Lap Kok could be removed with the opening up of airspace over the Pearl River Delta.
The Civil Aviation Department said officials from Hong Kong, Shenzhen and Macau had finally reached a consensus on relaxing airspace boundaries after three years of talks.
No formal agreement has yet been signed, but it is seen as a vital step if the three cities are to meet the demands of growing air traffic in the region in the next two decades.
Airlines in the greater Pearl River Delta are expected to be carrying 240 million passengers a year by 2030.
Without such an agreement, it would be impossible to fully utilise the new HK$136.2 billion runway, the Airport Authority said.