Satellite images have emerged that appear to back up claims China was massing troops on the border of Hong Kong.
The two photos, showing what looks like around 120 army or police trucks in a stadium in the Chinese mainland city of Shenzhen, came after a video purporting to be of troop movements in the same area was retweeted by Donald Trump on Tuesday night.
The satellite pictures, of the Shenzhen Bay Sports Centre, were taken on 12 August and was credited to Maxar technologies, a space technology firm based in the US.
The eight second clip of video that was retweeted by Mr Trump and widely circulated on social media, appeared to show dozens of trucks driving into the sports centre in western Shenzhen.
The sports centre is just off the main road that leads to one of the key access roads to Hong Kong, where anti-China protests have intensified in the last few days.
On Tuesday night, protesters clashed with security forces at the airport in Hong Kong, which is administered independently from China but is Chinese territory.
Rumours had been circulating for several days that the Chinese were preparing for an assault on the protests, sparking fears of a major crackdown.
It is not known if the trucks are still at the Bay Sports Centre as cloud cover is preventing more up to date images.
A handful of people on Chinese social media site Weibo have mentioned military activity in the area in the last 24 hours, but Sky News has not been able to verify this.
The video Mr Trump retweeted was first put on Twitter two days ago by Alexander Krauss, a senior political adviser to Renew Europe, the liberal group in the European Parliament.
He said on 12 August: "Disturbing video taken in #Shenzhen just across the boarder with #HongKong. Something extraordinarily bad is about happen. #China #HongKongProtests #Democracy #SaveHongKong."
Sky News has identified the spot from where the video was shot as a concourse, leading up to the stadium, above Binhai Avenue Side Road.
The level of development shows that it was almost certainly filmed after January 2019, as one of the buildings in the shot was only finished earlier this year.
Earlier, Mr Trump had tweeted: "Our Intelligence has informed us that the Chinese Government is moving troops to the Border with Hong Kong. Everyone should be calm and safe!"
Chinese state media has only said the exercises were planned previously and were not directly related to the unrest in Hong Kong.
But the government in Beijing has hardened its rhetoric in the last few days saying the protesters were beginning to show the "sprouts of terrorism", after the airport had to be closed.
Secret China website reported on 11 August that a large-scale anti-riot rehearsal had been photographed by a number of people, with a "large number" of armed police gathering in east and central Shenzhen and other districts.
The site claimed Shenzhen's Public Security Bureau had gathered 12,000 police officers to conduct training in the Baoan District Waterfront Plaza, about 6km (3.7 miles) from the stadium.
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It reported that one Weibo user had seen a number of armed vehicles and more than 200 units of armed officers.
Hong Kong has featured widely in pro-China state media in the last few days, with the China Global Times reporting on a "brutal attack" by protesters on one of its reporters at Hong Kong's airport.
The reporting, along with widespread sharing on Chinese social media of the treatment by demonstrators of the reporter and another "visitor", has fuelled speculation of a possible intervention in Hong Kong.