National security police on Thursday arrested a 24-year-old man at the airport, linking the move to the arrest of four others the day before.

Sources said the latest man arrested is Calvin Chu, a former standing committee member of the now-disbanded Demosisto group.

All five men arrested are suspected of colluding with foreign forces to endanger national security and sedition offences, police said.

"Investigation revealed that the arrested person was suspected of having connection with the group of people arrested on Wednesday," the force said in a statement.

One of those arrested on Wednesday was believed to be Ivan Lam, who is also a former Demosisto member.

Police earlier said the first four men arrested were suspected of receiving funds to support people who had "fled overseas" and who had "continued to engage in activities that endanger national security".

Former Demosisto leader Nathan Law was named by police earlier in the week as they offered HK$1 million rewards for the capture of eight national security law suspects overseas.