A fourth straight day of protests drew hundreds of thousands of people across Lebanon on Sunday, emboldened by the potential collapse of the country's ruling coalition.

The capital, Beirut, Tripoli in the north and the southern port of Tyre came to a standstill, with demonstrators waving Lebanese flags and chanting: "The people want to bring down the regime."

Protesters say they have had enough of a ruling class that has divvied up power among themselves and amassed wealth for decades but done little to fix a crumbling economy. Worse still, the government plans a further program of austerity.

Footage posted to social media showed a huge crowd gathered in Beirut's main square.

Sunday's protests, the largest thus far, took place following the resignation a day earlier of a key Christian party's four ministers and amid a threat by Prime Minister Saad Hariri that he would otherwise step down.

Read more: Lebanon: Bikini model scandal amid economic crisis threatens PM

Reuters news agency reported that late on Sunday, Hariri and his government partners agreed to an economic reform package that he hopes will alleviate the crisis. He had been struggling to get his political rivals to agree on several austerity measures to avoid a deeper crisis and unlock over $11 billion (€9.9 billion) in economic assistance pledged by international donors last year.

Hariri had given his partners until Monday evening to back key reforms, which include taxes on banks and a plan to overhaul the state electricity firm.

On Saturday, the head of the Christian Lebanese Forces quit, saying the party was "convinced the government is unable to take the necessary steps" to solve the crisis.

If Hariri, a Sunni Muslim who is traditionally backed by the West and Sunni Gulf Arab allies, resigned, it would be harder for the various parties that make up the ruling coalition to form a new Cabinet.

A new government would also likely see the Iranian-backed Hezbollah and its allies win more power, a shift that would make it nearly impossible for international donors to offer aid or investments.

Hezbollah chief Hassan Nasrallah warned on Saturday that a change in government would only worsen the situation.

Read more: Hezbollah: What good would a German ban do?

The four days of protests that have rallied tens of thousands of people were triggered in part by a proposed 20-cent (€0.18) daily charge on voice calls made through WhatsApp, a measure that was quickly scrapped but that was seen by many as the latest government attempt to squeeze the already struggling public. A quarter of Lebanon's population lives below the poverty line.

The demonstrations have brought together people from across the sectarian and religious lines that define the country and its political system, including Christians, Sunni Muslims, Shiite Muslims and Druze. They are the largest protests to take place in the past five years.

"I didn't expect people from the country's north, south and Beirut to join hands and like each other. The protests have brought together everyone and this has never happened before," said Sahar Younis, a 32-year-old worker with a nongovernmental organization.

"We want to stay in Lebanon to build our future, but if these corrupt politicians stay here, what future will be left for us?" 17-year-old student Cherbel Anton said.

The Association of Banks in Lebanon announced that all banks would be closed on Monday because of the unrest.

Read more: Lebanon faces race against time to avoid financial collapse

Lebanon's public debt ratio is one of the largest in the world — more than 150% of gross domestic product, or around $86 billion — according to the Finance Ministry.

Growth has plummeted in recent years, with political deadlock compounded by the impact of eight years of war in neighboring Syria.

mm, es/tj (AFP, AP, dpa, Reuters)

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