Hong Kong police say they have arrested at least 13 people who took part in Monday’s pro-democracy protests, including one man accused of ransacking Hong Kong’s Legislative Council building with hundreds of other protesters who vandalized offices and the main chamber.

The man, surnamed Poon, was arrested in Hong Kong's Mong Kok neighborhood on charges of assaulting police, criminal destruction, public misconduct and forced entry into the Legislative Council Complex, authorities said.

CHINA SAYS PROTESTERS' STORMING OF HONG KING GOVERNMENT BUILDING 'TOTALLY INTOLERABLE'

The 12 others -- 11 men and one woman -- were arrested in relation to a different protest that took place Monday morning. They face various charges including possession of offensive weapons, unlawful assembly, assaulting a police officer, obstructing a police officer and failing to carry an identity document. \

Monday's unrest began when protesters rushed police barricades at the time of a morning flag-raising ceremony marking the 22nd anniversary of Hong Kong’s handover to China from Britain. Police used shields, batons and pepper spray to keep the crowd at bay.

That evening, protesters broke into the parliamentary building, occupying the main chamber of the Legislative Council and vandalizing property. Police initially retreated to avoid confrontation and gave the demonstrators the run of the building. For a few hours, protesters defaced portraits of lawmakers and spray-painted pro-democracy slogans in the chamber before being evicted by security forces.

Workers and authorities began cleaning up the aftermath on Wednesday, boarding up shattered windows and carting away evidence in what will be a massive sweep and criminal investigation. At almost every turn of the parliamentary building, slogans had been spray-painted on the walls in Chinese and English; “Destroy the Chinese Communist Party,” read one, while another said, “Hong Kong is not China.”

ANDY PUZDER: HONG KONG PROTESTERS ARE FIGHTING FOR THEIR FREEDOM -- THEY DESERVE US SUPPORT

Steve Vickers, a former head of criminal intelligence for the Royal Hong Kong Police, predicted a nearing government crackdown that will result in long jail terms.

"I am personally sympathetic to the great majority of the Hong Kong demonstrators and their motivation, but the hardcore elements and agitators involved are becoming increasingly desperate," Vickers told the Associated Press. "Their actions are counterproductive to many Hong Kong peoples' genuine democratic aspirations."

Protesters are demanding an independent investigation into the police crackdown on protests last month, which was harsher than usual for Hong Kong. Authorities, however, said it was justified after some protesters turned violent.

CLICK HERE TO GET THE FOX NEWS APP

Millions of citizens have taken to the streets in recent after Hong Kong Chief Executive Carrie Lam attempted to pass an extradition bill that would allow criminal suspects apprehended in Hong Kong to be extradited to mainland China for trial. Experts say the bill puts critics of China’s ruling Communist Party at risk of torture and unfair trials in the mainland, and further chips away at the judicial independence and civil liberties Hong Kong was promised after the 1997 handover.

While Lam has shelved the bill, she has not agreed to abandon it as protesters demand. Further demonstrations have demanded Lam’s resignation and subsequent election for a new city leader, but she has refused to address those requests.

Fox News' Morgan Cheung and the Associated Press contributed to this report.