Massive protests calling for an immediate cease-fire were staged in Brussels and many other European cities on Saturday against Israeli military operations in Gaza that have triggered a humanitarian crisis.

An estimated 21,000 people turned out in Brussels despite rain, marching from the city's North Station to the Central Station, according to initial statistics by the local police.

"Cease-fire now!", "Free Palestine", "Stop the genocide" and "Boycott Israel" were some of the slogans shouted and on banners held by protesters.

Some held banners criticizing US and European Union leaders for their endorsement of Israel's actions and their persistent refusal to call for a cease-fire.

Many demonstrators waved Palestinian flags and wore kaffiyehs, or the black and white scarf symbolizing the Palestinian cause. Some held photos of children killed in Israeli bombings and some carried baby dolls covered in blood.

The organizers said there is "the urgent need to ensure that international law is respected … and demand an immediate cease-fire to save human lives".

"How can we defend the two-state solution while refusing to sanction the occupation and colonization (of Palestine) or refusing to recognize the state of Palestine now?" Simon Moutquin, a Green Party member of the Belgian Parliament, said in a message on X after attending the demonstration.

In London, organizers said 800,000 people took part in Saturday's demonstration and called it one of the largest demonstrations in British history, while the Metropolitan Police put the number at 300,000.

The protesters wanted to pressure British Prime Minister Rishi Sunak and Labour Party leader Keir Starmer who have not supported the call for a cease-fire.

In Paris, thousands of people marched from the Place de la Republique toward the Place de la Nation on Saturday to demand an immediate cease-fire in Gaza.

French President Emmanuel Macron told the BBC on Friday that Israel must stop bombing Gaza and killing civilians, a message that most Western leaders have refused to express.

"De facto, today, civilians are bombed, de facto. These babies, these ladies, these old people are bombed and killed. So there is no reason for that and no legitimacy. So we do urge Israel to stop," Macron said.

"Macron finally uttered the word 'cease-fire' but France must speak with a stronger voice, especially in the UN Security Council in which it is a permanent member," said Mathilde Panot, an MP and leader of La France Insoumise group in parliament.

"France must apply as much pressure possible on Netanyahu's far-right government in order to stop war crimes," she said.

Agencies contributed to this story.