National security police on Friday said they had arrested a man, 77, in Cheung Sha Wan on suspicion of "attempting to do or making any preparation to do an act or acts with seditious intention".

Sources said the suspect is Koo Sze-yiu.

Police said the arrestee had been detained for further enquiries and an investigation was underway.

"Members of the public are urged not to defy the law," the force said in a statement.