Government supporters stormed the Venezuela's opposition-controlled National Assembly, injuring several lawmakers and journalists.
The violence unfolded while President Nicolás Maduro was giving a speech at a government-planned Independence Day military parade in the capital, Caracas.
The supporters were armed with sticks and bars. Some set off fireworks within the building’s gardens. Photos of the walls of the building smeared with blood have circulated online.
Pro-opposition Venezuelan website La Patilla reported that several deputies had been attacked by a mob at the building in the capital.
It said there were "several injured inside the AN (National Assembly) who were beaten by violent groups".
Video from the scene showed people with blood running down their faces.
One of the wounded politicians, Americo de Grazia, had to be taken in a stretcher to an ambulance suffering from convulsions, said a fellow congressman.
Local media reports that eight have been wounded and it is believed at least one person has been taken away for medical treatment.
A large crowd had been gathered outside the building for several hours before dozens of them broke into the grounds.
The attackers ordered journalists to stop filming and taking photographs and leave the premises.
Venezuela is in a deep economic crisis and citizens face severe shortages of basic supplies such as medicine and food. The falling price of oil, which accounts for about 95% of export revenues, has made the situation worse.
An attempted takeover of the National Assembly by the Supreme Court earlier this year was reversed by the president, of whom there are almost daily protests calling for him to stand down. He has accused the opposition of trying to illegally overthrow the government.