Riot police have fired tear gas at demonstrators trying to break through a barrier to get to the parliament building in Beirut during a protest over the government's handling of this week's devastating explosion in the city.

About 7,000 people gathered in Martyrs' Square in the city centre, 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.

The protesters chanted "the people want the fall of the regime," and held posters saying "Leave, you are all killers."

"We want a future with dignity, we don't want the blood of the victims of the explosion wasted," said Rose Sirour, one of the demonstrators.

Tuesday's blast in the port, the biggest explosion in Beirut's history, killed 154 people, injured 5,000 and destroyed a swathe of the city.

The government has promised to hold those responsible to account.

Some residents, struggling to clean up shattered homes, complain the government they see as corrupt - there had been months of protests against its handling of a deep economic crisis before this week's disaster - has let them down again.

"We have no trust in our government," said university student Celine Dibo as she scrubbed blood off the walls of her shattered apartment building. "I wish the United Nations would take over Lebanon."

Several people said they were not at all surprised that French President Emmanuel Macron had visited their gutted neighbourhoods this week while Lebanese leaders had not.

"We are living in ground zero. I hope another country would just take us over. Our leaders are a bunch of corrupt people," said psychologist Maryse Hayek, 48, whose parents' house was destroyed in the explosion.

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Lebanon's Kataeb Party, a Christian group that opposes the government backed by the Iran-aligned Hezbollah, announced the resignation of its three politicians from parliament.

"I invite all honourable (politicians) to resign so that the people can decide who will govern them, without anybody imposing anything to them," said party chief Samy Gemayel, announcing the move during the funeral of a leading member of the group who died in the explosion.

Mr Macron, who visited Beirut on Thursday, promised angry crowds that aid to rebuild the city would not fall into "corrupt hands". He will host a donor conference for Lebanon via video-link tomorrow his office said.

The prime minister and presidency have said 2,750 tonnes of highly explosive ammonium nitrate, which is used in making fertilisers and bombs, had been stored for six years without safety measures at the port warehouse.

President Michel Aoun said yesterday that an investigation would examine whether it was caused by a bomb or other external interference.

Mr Aoun said the investigation would also weigh if the blast was due to negligence or an accident. 20 people had been detained so far, he added.

Some residents wondered how they would ever rebuild their lives.

Officials have said the blast could have caused losses amounting to $15 billion.

That is a bill that Lebanon cannot pay after already defaulting on a mountain of debt - exceeding 150% of economic output - and with talks stalled on a lifeline from the International Monetary Fund.

France and other countries have rushed emergency aid to Lebanon, including doctors, and tons of health equipment and food.

The blast destroyed Lebanon's only major grain silo and UN agencies are helping provide emergency food and medical aid.

Arab League Chief Ahmed Aboul Gheit said after a meeting with Mr Aoun that he would seek to mobilise Arab efforts to provide support to Lebanon.

Also speaking after meeting Mr Aoun, Turkish Vice President Fuat Oktay said his country is ready to help rebuild the port.

For ordinary Lebanese, the scale of destruction is overwhelming.

"It felt like a mini atomic bomb," said George Rohana, sitting beside a supermarket that was demolished.

Marita Abou Jawda was handing out bread and cheese tov ictims of the blast.

"Macron offered to help and our government has not done anything. It has always been like that," she said. "After Macron visited I played the French national anthem all day in my car."