Hong Kong police arrested a former senior journalist with the Apple Daily newspaper at the international airport on Sunday night on a suspected national security charge as he tried to leave the city, according to media reports.

Fung Wai-kong would be the seventh staffer at the pro-democracy Apple Daily newspaper to be arrested on national security grounds in recent weeks. He was an editor and columnist at the now-closed paper, Hong Kong media reported.

Police said in a statement that a 57-year-old man had been...