Thousands of people demonstrated in Paris and other major cities on Saturday under the rallying cry "Stop the massacre in Gaza". The left-wing organisers called for France to "demand an immediate ceasefire" between Israel and Hamas militants.
"I came to support the Palestinian cause, for a ceasefire in Gaza," said engineer Ahlem Triki, a Palestinian flag over her shoulders.
Hamas's shock 7 October attack killed about 1,200 people, mostly civilians, in Israel and 239 people taken hostage, according to Israeli officials.
The Israeli air and ground military campaign in response has left more than 11,000 people in Gaza dead, according to the Hamas-run health ministry.
"It is elementary that as activists or simple citizens, you go out on to the street to support the Palestinian people," said 85-year-old trade unionist Claude Marill.
French MPs Mathilde Panot and Eric Coquerel, whose hard-left France Unbowed (LFI) party has come under fire for an ambiguous stance on anti-Semitism, were present at the march.
Gaza ceasefire rallies also took place in other French towns including Marseille, Toulouse, Rennes and Bordeaux.
"This mobilisation is essential, in the face of massacres," said LFI coordinator Manuel Bompard at the demonstration of about 1,300 people in Marseille.
Elsewhere, more than 20,000 people marched through Brussels, some chanting "EU, shame on you" for perceived bias towards Israel at the expense of Palestinian lives and rights.
In London, police estimated that 300,000 people had turned out, 800,000 according to organisers.
Some 150 people from the mass protest were detained under public order legislation for wearing face coverings and setting off fireworks, while 82 counter-protesters were held to prevent them infiltrating the main march.
On the ground in Gaza, fighting has reduced some streets to ruins, with the sounds of apparent explosions and gunfire caught Saturday on AFPTV's Gaza City camera.
This comes as Israel pursues its offensive into Gaza City aimed at destroying the militant group Hamas in the territory it rules.
Tens of thousands of people have fled, many taking shelter in northern Gaza's hospitals which have been repeatedly hit by explosive strikes and gunfire.
"The hospital is besieged, with no option to bring in the corpses and injured people sprawled outside. There is no movement in or out of the hospital," said Physicians for Human Rights Israel, citing doctors at Al-Shifa Hospital.
The Israeli doctors' group added that due to an overnight power outage, the neonatal intensive care unit had stopped working and two premature infants had died, while leaving the lives of 37 other infants at risk.
The Israeli military has denied strikes or a siege at Al-Shifa hospital, and has repeatedly accused Hamas of using medical facilities as command centres and hideouts – a charge the group denies.
The Israeli army also said it would "provide the assistance needed" to help "babies in the paediatric department to get to a safer hospital" on Sunday, at the request of Al-Shifa staff.
Almost 1.6 million people have been internally displaced since 7 October, according to the UN agency for Palestinian refugees UNRWA – about two thirds of Gaza's population.