HONG KONG (AFP) - A 15-year-old was among five people arrested in Hong Kong under a sweeping national security law, police said Thursday (May 6), with local press reporting social media posts 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 scooped up on Thursday morning during raids looking for 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.

Beijing blanketed Hong Kong in a sweeping national security law late last June in response to months of massive and often violent democracy protests that convulsed the city.

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.