Forty-five people were injured by men in white t-shirts armed with baseball bats at Yuen Long station, with one in critical condition.
The developments come amid deteriorating relations between Beijing and London.
The demonstration was the latest against the government's controversial extradition bill.
It comes after former Canadian diplomat Michael Kovrig was detained in Beijing on Monday.
An explosion near the US embassy in central China has crowds gathering, yet people still queuing to get their Visa applications in.
No10 insists issue raised, but trade mentioned first.
Steel dumping and counterfeit goods warnings echo Trump
“We were super, super excited. Nobody had seen that before.”