Six people have been killed in clashes in Beirut over last year's devastating port explosion.
Violence erupted during a protest organised by the militant group Hezbollah and its allies against the lead judge probing the blast.
At least six people were killed and dozens wounded in some of the deadliest fighting in years, authorities said.
Gunfire echoed in the capital for several hours and ambulances, sirens wailing, rushed to pick up casualties.
Images on social media showed local schoolchildren hiding under their desks or gathered on the floor outside classrooms.
Tensions were high in Lebanon after the Iran-backed Hezbollah and its Shiite allies from the Amal Movement demanded the removal of the judge leading the investigation into last year's Beirut port explosion.
The two parties called for a protest near the Justice Palace, along a former civil war front line between Muslim Shiite and Christian areas.
The right-wing Christian Lebanese Forces also mobilised supporters on Wednesday evening
In a statement on Thursday, the two groups said their protesters came under fire from snipers deployed over rooftops in the Tayouneh area.
The subsequent armed clashes with the worst in Lebanon since 2008, when the Shiite Hezbollah briefly overran parts of Beirut.
Lebanon's Prime Minister Najib Mikati has appealed for calm and urged people "not to be dragged into civil strife".
The investigation into last year's explosion in Beirut focuses on hundreds of tonnes of ammonium nitrates that had been improperly stored at a port warehouse.
The explosion on August 4 killed at least 214 people, injured thousands, and several districts of the capital.
The blast further devastated a country already roiled by political divisions and unprecedented economic and financial meltdown.
The authorities have been accused by the victims' families of criminal negligence and refusing any international investigation.
Judge Tarek Bitar -- the second to lead the investigation into the explosion -- has been accused of singling out politicians for questioning, most of them allied with Hezbollah.
None of Hezbollah's officials have so far been charged in the 14-month-old probe. All have denied any wrongdoing.