Two radical anti-mainland traders' groups launched their third protest Sunday in Hong Kong's New Territories, provoking clashes with local residents and forcing shops to close.

The protest, called "Redeeming Yuen Long with valiance against violence," was organized by Civic Passion and Frontline Democracy. About 100 protesters dressed in yellow T-shirts marched from the Long Ping MTR station to Sau Fu Street, a shopping area popular with mainland tourists, Sunday afternoon.

Hundreds of policemen were deployed and dozens of observers and legal experts were present to monitor and record the protest.

During the protest, clashes occurred as some local residents expressed disagreement, and some had fought with the protesters, according to local media.

Police had to use pepper spray to separate the two groups. A woman was reportedly injured. A total of 33 people were arrested as of late Sunday.

Meanwhile, many shops were forced to close. The main road of Yuen Long was also paralyzed and buses had to take alternative routes.

The protest is the third in a month. Similar protests were launched in Tuen Mun and Shatin last month, causing chaos and injuries.

Frontline Democracy stressed Saturday that the protests were "necessary" after they claimed mainland shoppers were affecting the locals' livelihood.

Yuen Long District Councilor Leung Fuk-Yuen said Sunday he has not received complaints from the local residents against the mainlanders or traders.

A local resident surnamed Tong also told the Global Times that although mainlanders had caused inconvenience to local residents, and has indirectly increased the price of goods in the area, she does not agree with the protest as it is too radical.