HONG KONG • A 15-year-old was among five people arrested in Hong Kong under a sweeping national security law, police said, with local press reporting that social media posts had sparked their detention.

Officers from a specialist team in the financial hub arrested four males and one female aged between 15 and 24 on suspicion of subversion.

Local reports said three of those detained were nabbed on Thursday morning during raids that sought members of a group called "Returning Valiant".

"Their comments left on social media could constitute the offences of secession and subversion under the national security law," a police source told the South China Morning Post daily.

It was reported the raids stemmed from a burglary probe in which four others were arrested.

A statement posted on Facebook by "Returning Valiant" said some of its members were arrested under the national security law and that lawyers were looking into the situation.

"Political suppression will not make us step back... We will continue to fight against the tyranny," the statement added.

In July, four students including a 16-year-old were arrested over social media posts deemed to incite secession.

So far over 100 people - mostly pro-democracy politicians and opposition figures - have also been arrested under the new law targeting acts of subversion, secession, terrorism and foreign collusion. More than half of them have been prosecuted under the draconian law, which carries a maximum penalty of life imprisonment if convicted.

AGENCE FRANCE-PRESSE