HONG KONG — Thousands of protesters calling for democracy and some chanting "free Hong Kong" converged on the Chinese-ruled city's airport on Friday as Singapore advised its travelers to avoid protest areas in the territory.

Hong Kong airport authorities said operations at one of Asia's biggest civil aviation hubs would not be affected, but advised passengers to arrive early given the risk of disruption.

The former British colony, which returned to China in 1997, is embroiled in its worst political crisis for decades after two months of increasingly violent protests that have posed one of the gravest populist challenges to Communist Party rulers in Beijing.

The demonstrations, mushrooming almost daily, saw the defacement of China's main representative office last weekend, which Beijing said was an attack on China's sovereignty.

More protests are expected on Saturday with demonstrators outraged at an attack on Sunday at a train station by armed men who police sources say included some with backgrounds in Hong Kong's triad criminal gangs. Some 45 people were wounded.

Hong Kong returned to China under a "one country, two systems" formula, guaranteeing its freedoms — including rights to protest not enjoyed on the mainland — for at least 50 years.

What started as an angry response to a now-suspended extradition bill, which would have allowed defendants to be sent to the mainland for trial, now includes demands for greater democracy and the resignation of Hong Kong’s leader, Carrie Lam.

At the airport protesters, many dressed in black and seated on the ground, gradually filled the entire arrivals hall. They held up signs calling on the government to withdraw the extradition bill completely, while chants of "Free Hong Kong" reverberated around the cavernous glass and steel hall.

Organizers said some 15,000 people took part in the protest over 11 hours, while police put the figure at 4,000 at its peak.

"The world has been watching us in the past few weeks," said Jeremy Tam, a former pilot and lawmaker who helped organize the rally with other aviation sector employees.

"We simply believe that the airport is the most direct way for all tourists to explain what is happening in Hong Kong."

Tam read out an open letter from aviation employees saying they "felt furious" at "the pointless, non-constructive and sometimes misleading comments" given by senior government officials.

He said if the government did not respond to protester demands, "we do not rule out taking further actions such as (an) uncooperative movement".

An impromptu "tourist information" booth was set up by the protesters, with pictures and captions detailing the allegations of police brutality and the Yuen Long train station attack.

Some condemned the failure of police to protect citizens and protesters despite a flood of emergency calls.

"I think Hong Kong is a clean and safe city. The protest hasn't changed my idea of Hong Kong," said Sebastian Vanneste, 22, a tourist from New Zealand.

"I didn't know about the police brutality ... As a tourist, I respect Hong Kong people's freedom of speech and assembly."

Others, including tourists and pilots, flight attendants and other aviation workers, signed a petition urging the government to prosecute the attackers.

An application for a protest on Saturday in Yuen Long was rejected by police, but a sizeable turnout is still expected amid fears of clashes between triads and activists.

Singapore urged its citizens in a travel advisory to avoid parts of Hong Kong where protests may be taking place, noting the airport demonstration.

"You should take all necessary precautions to ensure your personal safety," it read. "Protests which are meant to be peaceful may still have the potential to turn violent with little or no notice."

The Flight Attendants' Union for Hong Kong's main carrier Cathay Pacific had earlier urged its members to "stand up for our human rights and be connected with the rest of the HongKongers" on its Facebook page.

"United Hong Kong Stands!" it added.

An investment banker at a US bank said he had rescheduled his flight from Hong Kong to Beijing to another day, over concerns flights could be grounded. — Reuters