What started out as peaceful marches across Hong Kong island and the Kowloon peninsula escalated into two days of clashes between protesters and riot police.

By Sunday night, the violence had intensified, with police firing tear gas into an underground station to disperse demonstrators.

Billy Li, a co-convenor of the Progressive Lawyers Group, told dpa that video footage of the tear gas showed “disproportionate use of force” as they were not under threat from protesters.

Elsewhere, video footage from Sunday showed police using batons and violent force to detain protesters although it was unclear how the conflict began.

One protester was seriously injured when a beanbag round, a non-lethal bullet used by police, hit her in the eye.

According to police, protesters responded by throwing bricks and a petrol bomb.

Hong Kong’s Hospital Authority said 40 people were injured over the weekend.

Police told dpa early Monday that they were still calculating the total number of weekend arrests, although 16 people were arrested on Saturday.

The airport sit-in on Monday marks the fourth consecutive day of protests in the airport, one of the world’s busiest, to raise international attention.

Protests began on June 9 against a now suspended legislative bill that would have allowed for criminal extradition to mainland China.

While Hong Kong returned to Chinese rule in 1997, it has – until 2047 – a separate legal system under the “one country, two systems” arrangement