A Hong Kong police officer was stabbed in the neck on Sunday in one of the worst acts of violence against the authorities during the 19th straight weekend of civil unrest in the global financial hub.

Graphic footage emerged of the policeman being stabbed in the neck from behind with a sharp object as his team retreated towards Kwun Tong metro station.

The police confirmed that two people had been arrested at the scene and the officer had been transferred to hospital “in a conscious state” and was stable.

A police source said that the officer had sustained a 3cm cut to his neck, and while it was still hard to confirm the extent of his injuries, that the attack was “one of the worst” when seen “in terms of malice, in terms of an attempt to kill the officer.”

Flash mob-style protests had initially peacefully in multiple locations with small groups of a few hundred people chanting “Free Hong Kong” slogans but soon developed into chaotic clashes with the riot police as more radical black-clad activists trashed shops and erected barricades on busy roads.

