Multiple sources say the protesters surged into Parliament's building, setting off vandalism and other acts.
Some reports say parts of the building had been set afire.
Video was shown to sources of a person ramming a bulldozer through a gateway, breaching security so protestors could get into the building's grounds. Others set official's cars afire and did other damage.
From the building, people, some waving the green flag of Kadhafi, scattered paperwork into the air.
Sources describe heavy smoke outside the building from burning tires. And the loud voices of those who came in rage against the government and the political factions whose fighting has brought this nation to a near standstill.
"We want the lights to work," protesters chanted, according to AFP.
Lawmaker Balkheir Alshaab told Libyan channel Al-Ahrar: "We must recognize our failure and immediately withdraw from the political scene."
Because Libya observes the Islamic week, Parliament was closed on Friday.
Libya's Parliament, the House of Representatives, is located a considerable distance fdrom the capital, Tripoli. It has been based there since the nation was fractured by the two clashing factions in 2014.
But in Tripoli, a competing legislative body called the High Council of State sits in representation of the partisans who hold that part of Libya.
This article was written with information provided by Reuters and Agence France-Presse