Grim developments in recent days suggest this is not going to end well.

Those developments include a significant escalation in the level of violence on both sides, the threat by Donald Trump to retaliate through trade if "bad things" happen in Hong Kong, the invocation of controversial "reserve powers" by Carrie Lam to ban face masks at protests and the arrival of even more People's Armed Police and People's Liberation Army personnel and resources.

Trump's gesture, while undoubtedly well-meant, could backfire badly. It appears to disrespect China's legitimate sovereignty over the island and could force President Xi Jinping into a face-saving gesture.

Xi Jinping is already under pressure at home over both the trade war and Hong Kong and is reportedly sick and tired of being made to look weak on the international stage.

The challenge for China, which regained possession of the former British colony after the expiration of a 100 year lease in 1997, and the protesters, is to negotiate a course that respects the mainland's sovereignty on the one hand and the democratic aspirations of the residents under the "one country, two systems" formula on the other.

Unless a third party is ready, willing and able to make a positive contribution to such an outcome it should leave well enough alone.

As matters stand, after almost 200 days of demonstrations the government and the protesters have never been further apart. The shooting, by police, of two young men during the same week Beijing was celebrating 70 years of communist rule was a Rubicon that cannot be recrossed.

Xi Jinping, through Carrie Lam, seemed to be telling the dissidents now his big day is over the gloves are coming off.

This reinforced Lam's decision to use the reserve powers to ban face masks. While the emergency laws may be unconstitutional that hasn't stopped police and security forces from implementing them with unprecedented force and vigour.

Protesters have responded with violence of their own, attacking police and infrastructure with petrol bombs and even sticks and rocks. The Metro, which was shut down for four days, was only just restored to limited operation on Tuesday morning local time.

This is a major blow given most residents depend on the service to get to and from work, schools and shops.

The long running standoff has already had a critical impact on the economy in a range of different ways. The Hang Seng, South East Asia's leading stock market, is down more than 14 per cent since May 3. Retail sales are down 23 per cent year-on-year and tourist numbers from the mainland are down 42 per cent.

Some commentators fear the equities market could be on the cusp of a free fall.

This would be just as devastating for Beijing, which uses Hong Kong as its commercial gateway to the world, as it would be for the island and its people.

There are also fears President Xi Jinping may decide to cut his losses and use the 6000 PLA/PAP personnel already on the island to crack down hard.

"One thing that might be driving his thinking is that he will look at (the 1989 Tiananmen massacre) and see how quickly international engagement recovered afterwards in terms of the economy," Malcolm Davis of the Australian Strategic Policy Institute said.

Mr Davis said unless both sides stepped back from the brink "things are going to slide towards some sort of military or People's Armed Police Intervention".

That has to be avoided at all costs.