Hong Kong’s chief executive Carrie Lam has condemned this week’s extraordinary mass protests in the former British colony, warning that “violence will not be tolerated”.

Police fired rubber bullets, tear gas and pepper spray at thousands of protesters on Wednesday as much of Hong Kong’s financial district erupted.

The Hong Kong Hospital Authority said 72 people were treated in hospital on Wednesday night.

Ms Lam told the ABC on Thursday that “these acts of rioting, which damage social peace and disregard the law, are intolerable”.

“Clearly, this is no longer a peaceful assembly but a blatant, organised riot, and in no way an act of loving Hong Kong,” she said.

Wednesday’s protests brought some of the worst violence in Hong Kong since Britain handed it back to Chinese rule in 1997.

It was the third night of demonstrations since a march on Sunday drew what organisers said was more than a million people to protest against an extradition bill that would allow people to be sent to mainland China for trial.

Overnight, thousands of protesters remained near the legislature in the Admiralty district. Thousands more retreated to the central business district.

By Thursday morning, the area was quiet, with government offices and banks shut for the rest of the week.

Security remained tight, with scores of uniformed police with helmets and shields in the area, while a long row of police vans was stationed alongside. Plain clothes officers checked commuters’ identification.

But only a few hundred protesters milled around. Some were sorting supplies of face masks and food as a widespread clean up took place.

See a gallery of photos from Wednesday’s violence

Police in Hong Kong fire rubber bullets, tear gas and pepper spray as thousands protest against the extradition bill. https://t.co/ElcA0T7U0H pic.twitter.com/xzck1a786R

— Al Jazeera English (@AJEnglish) June 12, 2019

While acknowledging the controversy, Ms Lam has refused to postpone or withdraw the bill. She and her officials say it is necessary to plug “loopholes” that allow Hong Kong to be a haven for criminals wanted on the mainland.

She accused protesters of carrying out “dangerous and even life-threatening acts” and told them to “calm down”.

“If a goal can be reached by radical and violent means, such scenes will become more severe, which will definitely put Hong Kong in harm’s way,” she told the ABC.

But opponents, including leading lawyers and rights groups, say China’s justice system is marked by torture and forced confessions, arbitrary detention and poor access to lawyers.

In an impromptu media stand-up in the legislature on Thursday, Democratic politicians strongly criticised Ms Lam’s heavy-handed police response.

“We are not a haven for criminals, but we have become a haven of violent police. Firing at our children? None of the former chief executives dared to do that,” said legislator Fernando Cheung.

“But ‘mother Carrie Lam’ did it. What kind of mother is she? I have never seen such a evil-hearted mother.”

A worker clears away the debris from the protests on Thursday. Photo: Getty

Concerns over the unrest prompted Hong Kong’s Tourism Board to call off its Dragon Boat Carnival this weekend.

Hong Kong’s benchmark stock exchange slid 1.5 per cent in early trade on Thursday, extending losses from Wednesday afternoon.

Australia’s Foreign Minister Marise Payne has also urged protesters and authorities to avoid further violence.

“Australia supports the right of people to protest peacefully and to exercise their freedom of speech, and we urge all sides to show restraint and avoid violence,” she said on Thursday.

Australia’s Consul-General in Hong Kong has raised concerns about the proposed laws at “senior levels” within the Beijing-backed government.

The European Union has said in a statement it shared many of the concerns raised by citizens of Hong Kong regarding the proposed bill and called for in-depth inclusive public consultation on the issue.

-with AAP