Legislators in Hong Kong have thrown objects including a glass of water at the former British colony' chief executive, Leung Chun-ying, while others have protested by holding up signs demanding democratic reforms.
Thursday's incident within the Legislative Council occurred a day after hundreds of police dragged pro-democracy activists from the Asian financial hub's central business district and arrested more than 500.
The glass did not hit Leung, but after the incident he accused legislators of using "abusive language" and taking "increasingly radical actions".
During an annual demonstration on July 1 to mark the 17th anniversary of Hong Kong's return to China, hundreds of thousands of demonstrators called on Leung to resign, saying he has failed to serve the territory's people.
Leung, who has rejected the calls to stand down, expressed his regret over the incident and his office released a statement saying it had contacted the police.
A police spokesperson said in an email to Reuters news agency that no arrests had been made, although they were investigating the incident.
Some of the legislators said they were angry about how the Hong Kong government had handled a recent decision to fund two new towns, while others were protesting against the government's failure to respond to an unofficial referendum on democracy in which nearly 800,000 voted.
The referendum was followed by a pro-democracy march on Tuesday. More than 1,000 people protested in an overnight sit-in at Hong Kong's Central business district.
Hong Kong became a special administrative region of China in 1997 after the British transferred sovereignty to China.
It is governed under a "one country, two systems" policy in which it has wide-ranging autonomy including a separate legal system.
Pro-democracy activists, however, say China is failing to make good on its promise of universal suffrage. They want elections in 2017 in which everyone can cast a vote for the chief executive.
The stand-off intensified last month when China published an unprecedented cabinet-level white paper reasserting its control over Hong Kong.