The Democratic Party said he was attacked by three assailants, one of whom filmed the incident, reports Efe news.
Kwong, who is conscious, underwent a brain scan and cervical spine X-ray at the Tin Shui Wai Community Health Centre, his team added.
The attack on one of the popular faces associated with the huge protests gripping the city for the last 16 weeks took place at 10.00 a.m. in a parking lot in the Tin Shui Wai area of Hong Kong.
According to the South China Morning Post, Kwong was mediating between the protesters and the police.
"I do think it was a planned attack, trying to send a message to threaten all the legislative councillors in the pro-democracy camp and the organizers of the (anti-extradition movement) and those taking part in it," the SCMP quoted Lam Cheuk-ting as saying.
Another Democrat, James To Kun-sun, added that Kwong was one of the highest voted leaders.
"Beating up the most popular legislator sends an alarming signal to Hong Kong and the whole world that Hong Kong is no longer a place with rule of law," he told the SCMP.
This is not the first attack on a members of the pro-democracy movement.
In August, one of the leaders of the Civil Human Rights Front, Jimmy Sham Tsz-kit and his assistant Law Kwok-wai were attacked with a baseball bat and a stick in Kowloon, while vice-chairman of Demosisto, Isaac Cheng La-long was attacked by three men on Sep.2.
The protests, sparked in June in opposition to a controversial extradition bill, have gone on for more than 100 days in the special administrative region and have turned into a movement that seeks to improve the mechanisms of democratic governance in opposition to Beijing's perceived authoritarianism.
( With inputs from IANS )