The incident occurred at around 8.50 am when a group of protesters were trying to walk to join the rally at the Royal Plaza organised by the so-called Pitak Siam group.
They could not reach the rally site because of barriers installed by police at Makhawan Rangsan Bridge so that they forced to open the way by removing the concrete block and tried to break through more than 20 companies of police blocking the way.
Both sides scuffled and police hurled tear gas to disperse the protesters, while the protesters responded by throwing water bottles at the police.
Police told protesters to use other routes to enter the Royal Plaza via Wat Benjamabopitr and the 1st Division King's Guard.
Some 132 people were reportedly detained by police while 10 were reportedly injured, mostly from tear gas, including four police officers.
Police spokesman Pol Maj Gen Piya Uthayo said that the police were forced to use tear gas because the protesters were trying to break through the barrier, and that the police have tried their best to avoid clashes.
Meanwhile, Pitak Siam leader Gen Boonlert Kaewprasit said the police actions against the protesters is considered "improper" as they are unarmed.
Gen Boonlert said his group needs about three hours to assess the situation whether the protest will be intensified or not and are waiting to see if more people will join the rally.
He claimed that those who planned to join the protest are now being blocked from entering the main rally site.
Gen Boonlert said about 1,400 security guards of the Pitak Siam group have been deployed around the rally venue under the supervision of Gen Natthachai Permsap, a leading Pitak Siam member, who will coordinate with police on security issues.