Lebanese Prime Minister Najib Mikati has announced a day of mourning for Friday, a day after deadly fighting erupted in Beirut.

At least six people were killed and 32 others injured when gunfire broke out in the Lebanese capital.

It began during a protest by the Shia Muslim groups Hezbollah and Amal against the judge investigating last year's huge blast at the city's port.

They say snipers from the Christian Lebanese Forces (LF) shot at crowds.

The LF faction has denied instigating what was some of Lebanon's worst violence in years.

"We will not allow anyone to take the country hostage to their own interests," the country's President Michel Aoun said.

Huge tension surrounds the inquiry into the port explosion that killed 219 in August 2020.

Swathes of the city were devastated by the blast, but no-one has yet been held accountable.

Hezbollah and its allies say the investigating judge is biased, but the victims' families support his work.

What began as a protest outside the Palace of Justice - the main court building - by hundreds of people arguing the investigation had become politicised and demanding the removal of Judge Tarek Bitar quickly escalated.

Heavy gunfire erupted in the streets as the crowd passed through a roundabout in the central Tayouneh-Badaro area.

Local residents had to flee their homes and schoolchildren ducked for cover under their desks as men armed with automatic rifles and rocket-propelled grenade launchers - believed to have been members of Shia and Christian militias - exchanged fire in the streets.

The clashes continued for several hours before calm was restored.

At a nearby school, teachers instructed young children to lie face down on the ground with their hands on their heads, a witness told Reuters news agency.

Hospital and military sources said some of those killed had been shot in the head. They included a woman who was hit by a stray bullet while inside her home.