HONG KONG — Pro-democracy protesters, some wearing surgical masks and holding up umbrellas to protect against tear gas, expanded their rallies throughout Hong Kong on Monday, defying calls to disperse in a major pushback against Beijing’s decision to limit democratic reforms in the Asian financial hub.

Police officers tried to negotiate with protesters camped out on a normally busy highway near the Hong Kong government headquarters that was the scene of tear gas-fueled clashes that erupted the evening before.

An officer with a bullhorn tried to get them to clear the way for the commuters. A protester, using the group’s own speaker system, responded by saying that they wanted Hong Kong Chief Executive Leung Chun-ying to demand a genuine choice for the territory’s voters.

“Do something good for Hong Kong. We want real democracy!” he shouted.

China has called the protests illegal and endorsed the Hong Kong government’s crackdown. The clashes — images of which have been beamed around the world — are undermining Hong Kong’s image as a safe financial haven, and raised the stakes of the face-off against President Xi Jinping’s government. Beijing has taken a hard line against threats to the Communist Party’s monopoly on power, including clamping down on dissidents and Muslim Uighur separatists in the country’s far west.

The mass protests are the strongest challenge yet to Beijing’s decision last month to reject open nominations for candidates under proposed guidelines for the first-ever elections for Hong Kong’s leader, promised for 2017. Instead, candidates must continue to be hand-picked by Beijing — a move that many residents viewed as reneging on promises to allow greater democracy in the semi-autonomous territory.

With rumors swirling, the Beijing-backed and deeply unpopular Leung reassured the public that speculation that the Chinese army might intervene was untrue.

“I hope the public will keep calm. Don’t be misled by the rumors. Police will strive to maintain social order, including ensuring smooth traffic and ensuring the public safety,” Leung said. “When they carry out their duties, they will use their maximum discretion.”

The protest has been spearheaded largely by student-age activists but has gathered momentum among a broad range of people, from high school students to the elderly.

Protesters also occupied streets in other parts of Hong Kong Island, including the upscale shopping area of Causeway Bay as well as across the harbor in densely populated Mong Kok on the Kowloon peninsula. The city’s transport department said roads in those areas were closed.

More than 200 bus routes have been canceled or diverted in a city dependent on public transport. Subway exits have also been closed or blocked near protest areas. Authorities said some schools in areas near the main protest site would be closed.

Leung urged people to go home, obey the law and avoid causing trouble.

“We don’t want Hong Kong to be messy,” he said as he read a statement that was broadcast early Monday.

That came hours after police lobbed canisters of tear gas into the crowd Sunday evening. The searing fumes sent demonstrators fleeing, though many came right back to continue their protest. The government said 26 people were taken to hospitals.

To ward off tear gas, demonstrators improvised with homemade defenses such as plastic wrap, which they used to cover their face and arms, as well as umbrellas, goggles and surgical masks.

The protests began with a class boycott last week by students urging Beijing to grant genuine democratic reforms to this former British colony.

“This is a long fight,” business and law student Edward Yau, 19, said overnight. “The government has to understand that we have the ability to undo it if they continue to treat us like we are terrorists.”

When China took control of Hong Kong from the British in 1997, it agreed to a policy of “one country, two systems” that allowed the city a high degree of control over its own affairs and kept in place liberties unseen on the mainland. It also promised the city’s leader would eventually be chosen through “universal suffrage.”

Hong Kong’s residents have long felt their city stood apart from mainland China thanks to those civil liberties and separate legal and financial systems.

Beijing’s insistence on using a committee to screen candidates on the basis of their patriotism to China — similar to the one that currently hand-picks Hong Kong’s leaders — has stoked fears among pro-democracy groups that Hong Kong will never get genuine democracy.

University students began their class boycotts over a week ago and say they will continue them until officials meet their demands for reforming the local legislature and withdrawing the proposal to screen election candidates.

Students and activists had been camped out since late Friday on streets outside the government complex. Sunday’s clashes arose when police sought to block thousands of people from entering the protest zone. Protesters spilled onto a busy highway, bringing traffic to a standstill.

In a statement issued after midnight, the Hong Kong police said rumors that they had used rubber bullets to try to disperse protesters were “totally untrue.”

Police in blue jumpsuits, wearing helmets and respirators, doused protesters with pepper spray when they tried to rip metal barricades apart.

Thousands of people breached a police cordon Sunday as they tried to join the sit-in, spilling out onto a busy highway and bringing traffic to a standstill.

Although students started the rally, leaders of the broader Occupy Central civil disobedience movement joined them early Sunday, saying they wanted to kick-start a long-threatened mass sit-in demanding Hong Kong’s top leader be elected without Beijing’s interference.

Occupy Central issued a statement Monday calling on Leung to resign and saying his “non-response to the people’s demands has driven Hong Kong into a crisis of disorder.” The statement added that the protest was now “a spontaneous movement” of all Hong Kong people.

Police said they had arrested 78 people. They also took away several pro-democracy legislators who were among the demonstrators, but later released them.

A police statement said the officers “have exercised restraint and performed their duties in a highly professional manner.” It urged the public to not occupy roads so that emergency vehicles can get through.

Among the dozens arrested was 17-year-old Joshua Wong, who was dragged away soon after he led a group of students storming the government complex. Wong is a leader of the activist group Scholarism, which organized protests two years ago that forced the government to drop proposed Chinese national curriculum guidelines seen as brainwashing. He was released Sunday evening.