HONG KONG — Hong Kong police fired tear gas and pepper spray in failed efforts to disperse thousands of pro- democracy demonstrators who continue to blockade roads and besiege the government headquarters early this morning.

In the biggest clashes to rock the city for decades, anti- riot police wearing gas-masks and carrying batons and guns repeatedly skirmished with demonstrators who used face masks, goggles, plastic wrap and umbrellas to protect themselves. Crowds thronged central Hong Kong to support a student-led protest that entered a fourth day to oppose China’s plans to control the city’s 2017 leadership election.

Many ignored calls by some organizers to pull back at about 10:30 p.m. Saturday night, with thousands remaining at 3.30 a.m. Sunday. Some moved metal barriers to create barricades across major roads into the Central business district, while others slept or sat using their phones as the previously heavy police presence thinned. New protests sprang up overnight in the Causeway Bay and Mongkok shopping districts, where hundreds of people obstructed traffic.

“This is a sad day for Hong Kong,” Anson Chan, Hong Kong’s former No. 2 official, said in a statement. “Pictures of our police force firing pepper spray and tear gas into the faces of unarmed protestors will shame our government in front of the whole world.”

Hong Kong Chief Executive Leung Chun-ying urged protesters to disperse for the stability of the city, dismissing rumors that police had opened fire or that the government planned to call in the People’s Liberation Army, which the Chinese government used to crush the student-led Tiananmen Square pro-democracy protests in Beijing in 1989. The PLA has garrisons in Hong Kong but is rarely seen on the streets.

“Hong Kong’s stable development for so long has depended on everyone’s abiding by peace and respecting the law,” Leung said in a televised speech at 1 a.m. “We don’t want Hong Kong to be chaotic or for people’s daily lives to be affected.”

The protests threaten to disrupt one of the world’s most vibrant financial centers and a gateway to investment in China. More than half the companies on Hong Kong’s benchmark Hang Seng Index are from the mainland, driving the city’s $3.7 trillion stock market, the fifth-largest worldwide.

Thirty-four people were injured as of 11:45 p.m. Saturday night, the city’s hospital authority said.

Police said they arrested 78 people for offenses including forcible entry into government premises, unlawful assembly, disorderly conduct, and obstructing police officers.