BRUSSELS: The EU called Wednesday for the release of dozens of opposition figures arrested in Hong Kong and said it was eyeing possible further sanctions on China over its crackdown.

"We are currently analysing the situation to see how we might need to react. There are other possibilities open to us, sanctions for example," European Commission spokesman Peter Stano told journalists.

Stano said any sanctions would have to be agreed unanimously by the EU's 27 member states, as happened in July last year when the bloc slapped sanctions on Beijing for its National Security Law, used to stamp out dissent in Hong Kong.

Police in Hong Kong arrested 53 people on charges of "subversion" in early morning raids. Those detained were opposition politicians and activists.

"We call for the immediate release of the arrested people," Stano said.

Under a treaty China signed ahead of it taking back Hong Kong from British colonial rule in 1997, Beijing committed to maintain a "one country, two systems" approach guaranteeing relative autonomy in the territory for 50 years.