A Greek MP slapped a female politician in the face and threw a glass of water at another during a live television debate on Thursday.
The programme host says Ilias Kasidiaris, whose Golden Dawn party entered parliament for the first time in May, was locked in a room at the studio after the incident, but broke down a door and escaped.
A public prosecutor has ordered police to track him down and arrest him on charges of causing serious bodily harm, Reuters reports.
The television debate on ANTENA, a private television station, descended into chaos when Mr Kasidiaris threw a glass of water at Rena Dourou, a member of the Syriza party, and called her a "joke" after she mentioned his alleged involvement in an armed robbery.
Communist party deputy Liana Kanelli then threw a newspaper at Mr Kasidiaris, who called her a ''commie'', pushed her and slapped her.
Golden Dawn won 7% of the vote in May. Its support has slipped ahead of a repeat election on 17 June, but it is still expected comfortably to exceed the 3% threshold needed to win parliamentary seats.
Mr Kasidiaris is already due to stand trial on 11 June on charges of helping assailants attack a university professor in 2007.