Hundreds of thousands of people have taken part in street demonstrations in Lebanon today.

In what was the largest in four days of protests that have crippled the country and threatened the coalition government.

The protests showed no sign of letting up, a day before a deadline set by Prime Minister Saad Hariri for government members to rally around key reforms.

The capital Beirut, second city Tripoli in the north and the southern port of Tyre came to a standstill, with streets filled with protesters waving the national flag, chanting "revolution" or "the people demand the fall of the regime" - a common refrain of demonstrations in other parts of the Arab world.

Protests have grown steadily across the Mediterranean country since public anger first spilled onto the streets on Thursday evening in response to a proposed tax on calls via WhatsApp and other messaging services.

While the government quickly dropped the plan, the leaderless protests morphed into demands for a sweeping overhaul of the political system, with grievances ranging from austerity measures to poor infrastructure.

More than a quarter of Lebanon's population lives below the poverty line, the World Bank says, while the political class has remained relatively unchanged since the end of a devastating 15-year civil war in 1990.

The beleaguered Prime Minister has urged members of his coalition government to support him but four ministers from a Christian political party quit on Saturday.

Lebanon ranked 138 out of 180 in Transparency International's 2018 corruption index, while citizens suffer chronic electricity and water shortages.

Lebanon's political system was set up to balance power between the country's religious sects, including Christians, Sunni Muslims, Shiite Muslims and Druze.

But critics say it entrenches political patronage and pits citizens against each other along sectarian lines.

What some have dubbed the "WhatsApp revolution" has support from wide swathes of Lebanese society.

The protests have been mostly good-natured, with people singing or launching into traditional dabke dances.

In Beirut, a group of young demonstrators camped out in a paddling pool, while a couple of newly-weds joined the crowd in the town of Jiyeh south of the capital.

But while the demonstrators are largely united on what they oppose - with many condemning the entire political class as thieves and criminals - they lack a clear set of demands.

On Sunday, Lebanese abroad also gathered to demonstrate in Paris, Los Angeles and Washington.

Prime Minister Saad Hariri has not said what will happen if the government did not back key reforms by Monday night, with the 72-hour deadline widely mocked among protesters and on social media.