Hundreds of members of the People’s Armed Police could be seen at a Shenzhen sports stadium where parking lots were filled by more than 100 dark-painted paramilitary vehicles, prompting U.S. concerns they could be used to break up protests across the border in Hong Kong.

China reiterated on Wednesday that Hong Kong’s protests were “near terrorism” as more street clashes followed ugly and chaotic scenes at the airport two days ago, when protesters set upon two men they suspected of being government sympathizers.

Seventeen people were arrested on Wednesday, bringing the total number detained since June to 748, police told a news conference, adding that police stations have been surrounded and attacked 76 times during the crisis.

Police tactics are toughening after 10 weeks of increasingly violent confrontations between police and protesters have plunged Hong Kong into its worst crisis since it reverted from British to Chinese rule in 1997.

The protests represent one of the biggest populist challenges for Chinese President Xi Jinping since he came to power in 2012 and show no immediate signs of abating.

U.S. President Donald Trump tied a U.S.-China trade deal to Beijing resolving the unrest “humanely”, and suggested he was willing to meet Xi to discuss the crisis.

“I have ZERO doubt that if President Xi (Jinping) wants to quickly and humanely solve the Hong Kong problem, he can do it. Personal meeting?” Trump said on Twitter.