Kwong’s partymate Lam Cheuk-ting said the three attackers punched and kicked the legislator as he was walking to his car near the Hong Kong Wetland Park at around 10am.
Lam said one of the trio also filmed the incident.
Kwong had been taken to Tin Shui Wai Hospital for treatment after being kicked in the back of the neck, Lam said.
Police said they were looking for four people over the incident. A spokesman said Kwong suffered injuries to his face, neck, hands and feet.
The Democratic Party condemned what it said was clearly an organised attack aimed at silencing those who have shown support for the ongoing anti-government protests.
“They recorded the entire process of the attack. I do think that it is a planned attack, trying to send a message to threaten all the legislative councillors of the democratic camp and the other organisers and participants of the anti-evil law movement,” Lam said.
Kwong had become a familiar face at the many protests over the summer, often chanting slogans and calling for restraint on both sides.