About 600 red-shirt and yellow-shirt protesters clashed outside the Crime Suppression Division offices on Phahon Yothin road on Tuesday, and commuters were advised to avoid the area, reports said.
The rival protesters gathered after police summoned for questioning a former female teacher who publicly accused red-shirt key supporter Darunee Kritbunyalai of defaming the royal institution last month.
There were about 100 red-shirts and about 500 yellow-shirts outside the compound, the reports said.
According to the reports, the two sides confronted each other vociferously and threw bottles at each other, and a pickup truck of a red-shirt supporters was heavily damaged during the clash.
The reports said one of the protest groups held a sign that read 'We Love the King' while another group held a sign that said 'We Love the Prince'.
Police urged travellers to avoid the area at this time.
Ms Darunee, 63, earlier filed a defamation suit against the woman, who shouted at her and accused her of defaming the royal institution on Aug 31.