Joshua Wong turned 30 last monthImage: Olivier Douliery/AFP

Prominent Hong Kong pro-democracy activist Joshua Wong was sentenced on Thursday to 10 more years in prison on a charge of collusion with foreign powers, under the city's China-imposed national security law,

The 30-year-old, who is already serving a nearly five-year jail term for "subversion" under the controversial national security law, was expected to be freed in January next year.

Wong will now not be due for release until the end of 2036.

Wong was accused of conspiring with self-exiled activist Nathan Law and others to ask foreign countries, bodies, or individuals outside China to sanction or engage in other activities against the government.

This is a developing story. More to follow.