Retired Catholic cardinal Joseph Zen hosts a packed mass, hours after appearing in a Hong Kong court over charges linked to the city's pro-democracy protests.

One of Asia's highest-ranking Catholic clerics, he was among a group of prominent democracy advocates who were arrested for "colluding with foreign forces", an offence under Hong Kong's national security law.

"They are not free. Let's pray to the Lord to fill their hearts with peace at all times," Cardinal Zen prayed for those who couldn't attend the mass today.