One police officer was injured in the explosion, believed to have occurred between 08:00 and 08:30 local time (07:00-07:30 BST). His injuries are not said to be life-threatening.
Five people, including the rabbi, were inside the synagogue at the time, authorities said. President Emmanuel Macron said the incident was “a terrorist act”.
One eyewitness who, who asked to remain anonymous, told the BBC: “Just as we were coming round the last corner, there was a huge explosion, a fireball into the air.
“It was surreal, like a film. We didn’t go any further.”
French Prime Minister Gabriel Attal and Interior Minister Gérald Darmanin are expected to travel to the scene later on Saturday.
They have both condemned the attack, with Mr Attal calling it “an antisemtic act,” while Mr Darmanin said security around Jewish sites would be reinforced.
“I want to assure our Jewish fellow citizens and the municipality of my full support,” the interior minister added.
Both leaders said security forces were tracking down the suspect.
The French Jewish community already live under high security, with many synagogues and Jewish schools under police protection.
A January 2024 report by the Council of Jewish Institutions in France (CRIF) said there had been a nearly threefold increase of antisemitic acts in France between 2022 and 2023.
In May, police shot dead a man after a synagogue in the north-western city of Rouen was set on fire.
In 2015, two days after the attacks on the Charlie Hebdo magazine, four people were murdered in a hostage attack on a kosher supermarket.
The explosion comes amid heightened concerns for Europe’s Jewish community, after the latest survey from the EU’s Fundamental Rights Agency (FRA) published last month found that Jewish people in the bloc continue to face high levels of antisemitism.
More than 8,000 Jews in 13 EU countries, including Germany and France, were interviewed. 96% said they had encountered antisemitism in their daily life.
There has been widespread condemnation of the attempted arson attack across France’s political spectrum. Left-wing politician Jean-Luc Mélenchon called it an “intolerable crime”, while the far-right National Rally’s Jordan Bardella said it was “a criminal and antisemtic act”.
