At least 15 people, including four policemen, were injured in a clash between Congress workers and the police, at Brahmagiri, about 70 km from Bhubaneshwar on Thursday, minutes before a function to be attended by Orissa Chief Minister Naveen Patnaik.
Trouble began near the Gop square market area when Congress workers were prevented from showing black flags to Patnaik by the police.
The protestors threw stones at the police, who made a lathicharge to disperse them.
A dozen persons were injured in the lathicharge and four policemen in stone throwing, the police said.
The chief minister was to lay the foundation stone of canalisation and improvement of the command area of a barrage at nearby Gobardhanpur.
Prohibitory orders under section 144 CRPC were clamped at Brahmagiri after the clash.
The foundation laying function went off smoothly, however, amidst tight security.
Patnaik arrived at the venue by helicopter. He also addressed a public meeting near the site, the police added.