It is the fourth consecutive day that thousands of demonstrators have gathered in the airport and it is the biggest disruption to the territory since protests began in early June.
Hong Kong international airport is one of the busiest in the world and officials said the demonstration "seriously disrupted" airport operations.
In a statement on its website it reads: "Airport operations at Hong Kong International Airport have been seriously disrupted, all flights have been cancelled.
"All passengers are advised to leave the terminal buildings as soon as possible. Affected passengers they must please contact their respective airlines for flight arrangement."