Rabbi Chaim Kanievsky, a leading authority on Jewish law, died on Friday at the age of 94 in Bnei Brak, an ultra-Orthodox city near Israel's commercial capital.
Parting the huge crowd, dozens of police formed a phalanx around the van carrying the sage's body as the vehicle crept towards Bnei Brak's cemetery.
"(Kanievsky's) death is a huge loss for the Jewish people," Prime Minister Naftali Bennett wrote on Twitter, appealing to mourners "not to crowd together or push".
Police estimated the crowd in Bnei Brak at around half a million people. The force erected barricades around the cemetery to limit the number of people at the graveside.
Hours earlier, police closed off highways around Bnei Brak to regular traffic to accommodate fleets of buses ferrying mourners to the city.
Israel's Magen David Adom ambulance service was also on high alert, with memories still fresh of a stampede last May at a crowded Jewish religious festival in northern Israel in which 45 people were crushed to death.
Kanievsky, born in what is now Belarus, made headlines in Israel at the start of the COVID-19 pandemic for defying government authorities and saying that ultra-Orthodox schools must remain open. He later relented, saying preservation of human life outweighed traditional practices.
Ultra-Orthodox Jews make up about 12% of Israel's population of 9.4 million.
(Reporting by Jeffrey Heller; Editing by Mark Heinrich and David Clarke)
