Hundreds of mourners gathered in a Bondi synagogue for the funeral of Rabbi Eli Schlanger on Wednesday, a few blocks away from the beach where he was gunned down at a Hanukkah festival three days ago.

Rabbi Yehoram Ulman, Schlanger's father-in-law, told the service Jewish people should not be scared of visiting Bondi Beach in the wake of the mass shooting.

He said local rabbis would organise an event for the end of Hanukkah to light eight candles this Sunday at the scene of the tragedy.

Schlanger was killed at the "Chanukah by the Sea" event organised by Chabad of Bondi, where he was an assistant rabbi.

Fifteen people were killed in the mass shooting, allegedly carried out by a father and son.

Schlanger, 41, recently became a father for the fifth time.

He was born in Britain but had lived in Sydney for the past 18 years.

Rabbi Ulman repeatedly broke down in tears as he remembered his son-in-law.

"You became everything to me, my hands, my feet. Your dedication to me knew no limits, I could rely on you for everything," he said. "You were my son, my friend, my confidant...to go a day without you seems impossible."

The crowd of mourners spilled outside the synagogue.

Dozens who could not get a seat gathered at the front of the venue, spilling on to the footpath, and watched the funeral's livestream on their phones.

Prayers in Hebrew and English were read during the service, including one by his brother-in-law Rabbi Mendel Kastel.

Security was heightened at Bondi Beach, with a heavy presence of police as well as a contingent of private security guards and Jewish security services.

State police cordoned off the street leading to the synagogue and conducted bag searches of attendees and media.

Mourners, including many men wearing yarmulkes, were shown in the synagogue, on a livestream of the funeral.

New South Wales state Premier Chris Minns, who has backed calls for tougher gun laws, federal opposition leader Sussan Ley and local member Allegra Spender were at the funeral.

Australian Prime Minister Anthony Albanese was not at the service and said earlier on Wednesday he would attend funerals if he was invited.

One mourner Stan Gol, 44, said Schlanger was selfless, caring and would be dearly missed by his community.

Gol and Rabbi Ulman said Schlanger would often drive up to four hours each way to visit some of the state's prisons and meet with Jewish inmates.

"We miss him dearly. He was there for everyone, he didn't care whether you were wealthy or poor," Gol said outside the Bondi synagogue. (Reuters)