A pro-democracy protester was shot and at least 180 were arrested as violent clashes rocked Hong Kong streets Tuesday while China celebrated the 70th anniversary of communist rule.

Beijing marked National Day and "national rejuvenation" with a military parade and fireworks, but in Hong Kong tens of thousands of demonstrators held a "national grief" march. Some black-clad protesters clashed with police who fired water cannons, tear gas and even bullets to quell the crowd.

Fires burned on Hong Kong streets, subway stations were closed, and many shops were shuttered as police warned residents to remain in their homes.

Police chief Stephen Lo said more than two dozen officers were injured in a series of skirmishes with protesters in what he described as “one of Hong Kong’s most violent and chaotic days."

Lo said police, combating crowds throwing bricks and incendiary objects, fired a total of six live rounds throughout the day and night. Most were warning shots, he said.

President Donald Trump took note of the anniversary on Twitter, lauding Chinese President Xi Jinping but making no mention of Hong Kong: "Congratulations to President Xi and the Chinese people on the 70th Anniversary of the People’s Republic of China!"

In Hong Kong, a video recorded by a student group appeared to show several protesters hurling objects at pursuing riot police. One officer drew his gun and fired, and a protester collapsed as the others fled.

“The so-called National Day is a day for mourning. We are mourning those who sacrificed for democracy in China,” former lawmaker Lee Cheuk-yan told the South China Morning Post. “It’s 70 years of suppression. We mourn that, and we also condemn the fact that the Hong Kong government together with Chinese government denied the people of Hong Kong the right to democracy.”

Pro-democracy residents of Hong Kong have long accused China of slowly encroaching on their rights since Britain handed over the administration of the city in 1997. The issue ignited months of massive and increasingly violent protests earlier this year following a government proposal to change extradition laws to allow suspects in Hong Kong to be sent to mainland China to face trial.

The Hong Kong government withdrew the proposal, but protesters have seized the momentum to press demands for more freedoms – and investigations into police behavior during the protests.

Hours after the protester was shot Tuesday, Police Senior Superintendent Yolanda Yu Hoi-kwan said police were "saddened" that an 18-year-old man was shot near his left shoulder.

"A large group of rioters attacked police officers," she said. "As an officer felt his life was under serious threat, he fired a round at the assailant to save his own life and his colleagues’ lives."

She added that protesters have been repeatedly warned to stop breaking the law.

"The police force really did not want to see anyone being injured, so we feel very sad about this," she said. "We will strictly enforce the law."

What to know:Hong Kong braces for violence on eve of National Day celebrations

The Hong Kong government marked National Day quietly with a flag-raising and reception that were closed to the public. Meanwhile in Beijing, 60,000 gathered in Tiananmen for a gala after a military parade at which China unveiled its Dongfeng-41 intercontinental strategic nuclear missiles, dubbed the country's newest and most powerful nuclear war deterrent.

Related:Hong Kong protests violent again: Chinese flag trampled, street fires ignited

Among the revelers in Beijing was Hong Kong Chief Executive Carrie Lam, the target of much of the protesters' scorn in the semi-autonomous territory of more than 7 million people.

In a Facebook post, Hong Kong police warned the public to stay at home and out of the fray.

"There are riots across Kowloon, Hong Kong Island and the New Territories," the post read. "Rioters have started fires and committed mass property damage, injuring many people. Police urgently appeal to every member of the public to stay in safe places, avoid going outdoors and stay tuned to the latest situation."