Pressure was growing Sunday on Lebanon's government after a protest campaign spurred by a trash crisis gave political leaders a deadline to meet their demands.

"Your time is up," the "You Stink" campaign behind Saturday's huge demonstration in central Beirut said on Facebook.

At the mass rally, "You Stink" threatened to escalate its protest movement if the government does not meet the demands by Tuesday evening.

The ultimatum calls for a sustainable solution to a trash crisis that flared in mid-July, the resignation of Environment Minister Mohammad Mashnuq and new elections to replace a parliament in power since 2009.

On Saturday, tens of thousands of protesters gathered in the capital's iconic Martyrs Square to express their rage at endemic corruption in the government and lack of basic services, including power and water.

Men and women of all ages flooded the square in a rare example of non-partisan mobilisation in the divided republic.

"You Stink" organiser Lucien Bourjeily called the rally "a really big victory".

"It also shows us that it's a big responsibility for us. We have to achieve the demands that we have set out," he told AFP.

Newspapers on Sunday noted that for once the protest was organised by civil society instead of the divided political elite.

- 'Certainty of change' -

"The Saturday of the people," headlined As-Safir newspaper.

An-Nahar daily said the demonstration "points to the certainty of change... under the pressure of a street that has been freed of the division between March 8 and March 14".

It was referring to Lebanon's main rival political blocs. March 14 is supported by Washington and Riyadh, while March 8 is headed by Hezbollah, which has the backing of both Damascus and Tehran.

The protest movement was initially launched to demand a solution to the crisis that has seen rubbish pile up uncollected. But it has since expanded to call for a total government rehaul.

Bourjeily said he could not reveal what the "escalation" promised by his movement would be, but said "there would be a role for all citizens".

He said "You Stink" would meet later to discuss the next steps, "taking every possible scenario into consideration".

There has been no official government response to the ultimatum.

But Parliament Speaker Nabih Berri said the demands could only be met through "the preservation and activation of the government".

Speaking at a rally of his largely Shiite Amal movement, Berri also called for fresh dialogue to discuss the presidential vacuum and the work of the cabinet and parliament.

Druze leader Walid Jumblatt tweeted that Saturday's protest "expressed the true pains of the Lebanese citizen... that no party dares to respond to".

Political rivalries have undermined change in Lebanon for years.

The 128-seat parliament has twice extended its mandate since 2009, and has been unable to elect a president since May 2014.

Any effective work by the cabinet has been paralysed.

"For the first time in a long time, civil society has mobilised for social demands, and not for the demands of a political leader," An-Nahar wrote.

- 'We showed them' -

"Politicians always use the excuse that 'the people are sectarian'," Bourjeily told AFP.

"Yesterday we showed them that the people aren't sectarian and that they can rise up against the political class. A door has been opened that cannot be shut," he said.

Organisers insist that no party or figure is exempt from their criticism.

"We are against all of the political class. The slogan is, 'All of them, means all of them'," said Bourjeily.

Last weekend, violence erupted when some demonstrators threw fireworks and plastic bottles at security forces who retaliated with tear gas, water cannons, and rubber bullets.

Many have criticised the riot police's use of force, with Prime Minister Tammam Salam admitting it was "excessive".

Interior Minister Nuhad Mashnuq said the results of an investigation into the incident would be revealed on Wednesday.

In Lebanon, which suffered a devastating civil war between 1975 and 1990, power is shared among Christians and Muslims.

The president is traditionally a Maronite Christian, the premier Sunni Muslim and the parliament speaker a Shiite.

Many former warlords still play a key role in Lebanese politics, some in parliament and others in government.