Figting rages in the Lebanese port city of Tripoli.
At least three people have died in the clashes, which pitted minority Alawites against their Sunni Muslim neighbours.
The fighting raged through much of Saturday night, and sporadic gunfire could still be heard into the morning.
Lebanon deployed several armoured vehicles and set up checkpoints to halt the clashes.
The fighting underlines how violence in neighbouring Syria could spill over into Lebanon.
Syrian president Bashar al-Assad - an Alawite - has led a brutal crackdown on the 14-month insurgency at home - an offensive that has enraged many Sunnis in Lebanon.
Syria's Sunni majority are at the forefront of the uprising.
Andrew Raven, Reuters