Video report by ITV News Asia Correspondent Debi Edward
British travellers heading to Hong Kong have been warned their electronic devices could be checked at the border.
As anti-government protests continue in Hong Kong, the Foreign Office has updated its travel advice for people travelling there.
The online advice reads: "In light of ongoing protests and demonstrations in Hong Kong, there are reports of greater scrutiny from mainland authorities at border crossings between the mainland and Hong Kong.
"This includes reports that travellers' electronic devices have been checked at border crossings."
The advice also states: "You should be aware that the thresholds for detention and prosecution in China differ from those in Hong Kong."
It follows on from the British consulate worker Simon Cheng Man-kit, who went missing two weeks ago after going on a business trip to the mainland city of Shenzhen.
China said earlier this week Mr Cheng [had been placed in administrative detention in the city of Shenzhen for 15 days](http://Protests outside British Hong Kong consulate after staffer detained by China) for violating public order regulations.
Protests in Hong Kong began 11 weeks ago with calls to scrap a now-suspended extradition bill, but have now widened to include demands for full democracy and an independent inquiry into alleged police brutality at protests.
Supporters of Hong Kong's pro-democracy movement created human chains on both sides of the city's harbour, inspired by a historic protest 30 years ago in the Baltic states against Soviet control.
They linked hands at first, then many switched on their smartphone lights and held them up to create a row of white lights against the nighttime skyline.
Organisers hoped the chains, which traced three subway routes, would total 25 miles in length.
Amid the current political unrest, international and local companies are finding themselves forced to back Beijing.
The region's flagship airline Cathay Pacific was the first to succumb to the resignation of its regional's executive and several staff members have been sacked for supporting the protests.
A current Cathay Pacific cabin crew member told ITV News anonymously the extent of the restrictions they are facing on all communications from social media to one-on-one conversations
"We have no freedom at all anymore, if there's any record of us even talking about the protest, whether you are in uniform or not, or in your daily life, they can thoroughly fire you," he said.
Britain's banking giant HSBC makes half of its profits in Hong Kong and it is now among those accused of kneeling to China.
This week it paid for a newspaper advert which denounced the demonstrations.
Standard Chartered and other larger firms have also condemned any big challenges to China's sovereignty.
ITV News Asia Correspondent Debi Edward said companies in China are having to constantly walk on a tight rope.
She said: "It's no longer just about their bottom line, they're having to strike a difficult balance between keeping their workforce and satisfying Beijing."