Correspondents say lawmakers left the building after hearing gunshots.
The attempted vote followed the resignation of Abdullah al-Thinni, who stepped down as prime minister earlier this month after he and his family were targeted by militiamen.
Libya has been plagued by instability since armed groups toppled Muammar Gaddafi’s regime in 2011.
Earlier reports that several people had been wounded in the attack on Tuesday are unconfirmed.
It is unclear who was behind the disturbance.
Libya’s national congress has been stormed on dozens of occasions by gunmen over the past year and a half.
Congress members were deadlocked over the latest appointment of a new prime minister when the latest attack broke out.
They had already held one round of voting and selected two out of seven candidates.
The second round of voting has been postponed. Local media say it is now scheduled to take place on May 4.
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