China's military issues warning to protesters as laser light hits Hong Kong barracks

China's Hong Kong military garrison warned protesters on Sunday they could be arrested for targeting its barracks in the city with laser lights.

In the first direct interaction between the People's Liberation Army (PLA) and protesters, the PLA raised a yellow flag with the arrest warning written in large letters, said a Reuters witness.

As a few hundred protesters shone laser lights on the barrack walls, troops in fatigues on the roof of the building shone spotlights at protesters and used binoculars and cameras to monitor those in the crowd.

Elsewhere, Hong Kong police fired tear gas as protesters defied an emergency law and marched wearing masks through the Chinese-controlled city, witnesses said.

There was no obvious reason for the tear gas, as the rally at Pacific Place on Hong Kong island seemed peaceful, said one witness.

Tens of thousands of protesters wore face masks in defiance of colonial-era emergency powers that threaten them with a year in prison for hiding their faces.

Hong Kong police were bracing for two major protests, fearing a recurrence of Friday night's violent protests that saw the Asian financial centre virtually shut down the next day.