Mr Trump fired several shots across the bow of the fellow Security Council member, moving beyond his typical attacks against China on international trade, reports Channel News Asia.
'The world fully expects that the Chinese government will honour its binding treaty (and) protect Hong Kong's freedom and legal system and democratic ways of life,' the US President told the General Assembly.
'How China chooses to handle the situation will say a great deal about its role in the world and the future,' Mr Trump said during his third appearance at the diplomatic forum in New York.
It marked one of his most strident speeches on the situation in Hong Kong since massive anti-government protests broke out there three months ago. Mr Trump had largely left it to the State Department to demand respect for the handover treaty, which grants the territory a 'high degree of autonomy', its own judicial, legislative and executive system, and the protection of its 'way of life'.
He said the world was 'counting on President Xi (Jinping) as a great leader' who could resolve the crisis.
The US president also fired a shot across China's bow on international trade, declaring that the time of Beijing's 'abuses' of the system was 'over'.
'For years, these (trade) abuses were tolerated, ignored, or even encouraged,' he said, arguing that 'globalism' had caused world leaders 'to ignore their own national interests'.
Touting what he argued were the benefits of his tariff war with China, Mr Trump reiterated his hope that a trade agreement 'beneficial to both countries' could be struck.
'But as I said very clearly, I will not accept a bad deal for the American people,' he said.