A Lebanese protester waves the national flag during clashes with security forces in downtown Beirut, Lebanon on Saturday, following a demonstration against a political leadership they blame for a monster explosion that killed more than 150 people. Photo: AFP

Lebanese protesters stormed government ministries in Beirut and trashed the offices of the Association of Lebanese Banks on Saturday as shots rang out in increasingly angry demonstrations over this week's devastating explosion.

The protesters said their politicians should resign and be punished for negligence they say led to Tuesday's blast, the biggest ever to hit Beirut, that killed 158 people and injured more than 6,000, compounding months of political and economic meltdown.

A policeman was killed during the clashes, a spokesman said. A policeman at the scene said the officer died when he fell into an elevator shaft in a nearby building after being chased by protesters.

The Red Cross said it had treated 117 people for injuries on the scene while another 55 were taken to hospital. Policemen wounded by stones were treated by ambulance workers. A fire broke out in central Martyrs' Square.

Dozens of protesters broke into the foreign ministry where they burnt a portrait of Lebanese President Michel Aoun, representative for many of a political class that has ruled Lebanon for decades and that they say is to blame for its current mess.

"We are staying here. We call on the Lebanese people to occupy all the ministries," a demonstrator said by megaphone.

About 10,000 people gathered in Martyrs' Square, some throwing stones. Police fired tear gas when some protesters tried to break through the barrier blocking a street leading to parliament, a Reuters journalist said.

Police confirmed shots and rubber bullets had been fired. It was not immediately clear who fired the shots. 

Riot police shot dozens of teargas canisters at protesters, who hit back with firecrackers and stones.

TV footage showed protesters also breaking into the energy and economy ministries.

Lebanese Prime Minister Hassan Diab said the only way out was early parliamentary elections.

Tuesday's blast was the biggest in Beirut's history. About 21 people were still reported as missing from the explosion, which gutted entire neighborhoods.

The government has promised to hold those responsible to account. But few Lebanese are convinced. 

Some set up nooses on wooden frames as a symbolic warning to Lebanese leaders.

Reuters