While President Donald Trump suggested a meeting with Chinese leader Xi Jingping over the Hong Kong crisis, China called the protests "close to terrorism" as normal operations began to resume at the international airport, the BBC reports.

What's new: The Airport Authority said late Wednesday that any application to protest in the terminal must be made in advance with a "Letter of No Objection" to be obtained from police, as security was heightened in the area, per Reuters. CNN notes that nearly 1,000 flights were canceled this week over the massive protests at the airport, which saw riot police clash with activists. More protests are planned for Friday, Reuters notes.

These atrocities, which are lawless, trampling on human rights and inhumane, have completely gone beyond the bottom line of civil society, and is no different to terrorist."

— Statement by China’s Liaison Office in Hong Kong

Catch up quick: Protests at the airport escalated Monday when thousands of demonstrators packed the main terminal and transport exits Monday, per Reuters. On Tuesday, thousands defied threats from China and Hong Kong's leader Carrie Lam and packed the departure area and blocked security gates for a 5th consecutive day of airport protests.

Pepper-spray carrying riot police then entered the airport for the first time since the protests began and clashes erupted, according to the Washington Post. Clashes ensued into the night.

riot police then entered the airport for the first time since the protests began and clashes erupted, according to the Washington Post. Clashes ensued into the night. Paramilitary police were assembling across the border in Shenzhen — a move some see as a threat to protesters, per AP. Trump tweeted earlier Tuesday that U.S. intelligence had told him of the move, saying "Everyone should be calm and safe!"

across the border in Shenzhen — a move some see as a threat to protesters, per AP. Trump tweeted earlier Tuesday that U.S. intelligence had told him of the move, saying "Everyone should be calm and safe!" Lam told a news conference that the city was on "the brink of no return." She said "lawbreaking activities in the name of freedom" were damaging the rule of law and warned protesters were pushing Hong Kong to "an abyss."

that the city was on "the brink of no return." She said "lawbreaking activities in the name of freedom" were damaging the rule of law and warned protesters were pushing Hong Kong to "an abyss." The Hong Kong leader defended police amid brutality claims. Law enforcement admitted earlier that some officers posed as protesters during unrest on Sunday, according to the BBC.

Why it matters: The chaos at the airport marks a massive disruption to the Chinese-controlled territory's economy since protests started in June. The airport directly and indirectly contributes to about 5% of Hong Kong's gross domestic product, per Bloomberg.

The big picture: Hong Kong International Airport is one of the busiest in the world, with about 1,100 flights daily across nearly 200 destinations.

Police said they had detained 5 people over Tuesday's clashes, bringing the total number of arrests to more than 600 since protests began in June, according to Reuters.

What they're saying: Activists including Joshua Wong, the pro-democracy protest leader who became a symbol of Hong Kong's 2014 Umbrella Movement, apologized for the disruptions they had caused at the airport.

Go deeper: Hong Kong protests assert the freedoms China seeks to constrain

Editor's note: This article has been updated with more details on the demonstrations, airport developments and Lam's comments.