Gaza is a "concentration camp where genocide is taking place", the UN's top court has heard.
The claims were made by South African lawyers as they outlined their case, accusing Israel at the International Court of Justice (ICC).
South Africa also called on the ICC to order Israel to cease military operations in Gaza.
Israel will present its defence next. It has vehemently rejected the accusations as "baseless".
On a freezing day in The Hague, Netherlands, there was no lack of feeling in protesters' hearts.
"Palestine will never die!" said one passionate Palestine supporter.
The pro-Palestine rally was emboldened by what was going on inside the famous court next door.
"It is changing the course of history, I believe," one woman told Newshub.
"I do have faith that this might turn the tide," said Dr Mohammed Aleem from Health Workers for Palestine.
The landmark case at the ICC drew supporters from both sides of the war in Gaza.
Families of Israeli hostages travelled to the Netherlands to be a voice for those still held captive.
"People are talking about what Israel is doing, but Hamas is committing crimes against humanity every day," said one pro-Israel supporter.
The Hague was heavy with history and overflowing with fresh pain as protesters clashed outside the court. Dutch police were forced to intervene.
Meanwhile inside the wheels of justice took a turn.
For months, the world has watched in despair as thousands of Palestinians were killed.
Hundreds of thousands have also been displaced, starved of food, water, medicine, and fuel.
South Africa told the ICC that amounts to genocide, and it's urging the court to order an immediate halt to the attack on Gaza.
"For the past 96 days, Israel has subjected Gaza to what has been described as one of the heaviest conventional bombing campaigns in the history of modern warfare," said South African lawyer Adila Hassim.
Israel has slammed the allegation as "atrocious" and will argue self-defence when it presents its case next.
A final decision on whether Israel has committed genocide could take years, but the court could rule fairly quickly on South Africa's request for Israel to suspend its military campaign in Gaza.
However, the ICC has no power to enforce its ruling, so Israel could simply choose to ignore the outcome.
Russia ignored a similar ruling to stop the war in Ukraine, but Balkees Jarrah, associate international director of Human Rights Watch is hopeful Israel would respond differently.
"The fact they are here, they are represented and they are presenting their case is significant, it suggests that they see the court as a legitimate institution," he said.
The word of the world's top court would add significant weight to the mounting pressure on Israel.
