A knife-wielding assailant stabbed four people in a rabbi’s basement synagogue in Monsey, NY during a crowded Hanukkah celebration Saturday night, according to a law enforcement source.

The suspect fled the scene in a 2015 Nissan Sentra, driving over the George Washington Bridge into Manhattan — and was promptly arrested by the NYPD at 144th Street and Seventh Avenue in Harlem at midnight, the source said. He was identified by a police source as Thomas Grafton, 37.

The accused attacker was transferred back to Rockland County around 4 a.m. from the 32nd Precinct by State Troopers, the lead agency on the case.

One victim was left in critical condition in the attack, which happened at around 10 p.m. when a man walked into the basement synagogue in Monsey with a machete or similarly large knife and began attacking people, the source said.

Between 50 and 100 people were inside the synagogue, which is known locally as Rabbi Rottenberg’s Shul.

Those gathered had just lit the menorah on the second-to-last night of the holiday, according to Aron Kohn, 65, who was inside.

“He just took it (the knife) out and started to run at people,” Kohn said.

Kohn described a frantic scene inside, saying he threw whatever furniture he could lay his hand on at the maniac.

“I saw him stabbing people and I started throwing chairs and tables,” Kohn said.

After slashing four people inside — a fifth person was injured in the panic — the attacker attempted to enter the temple next door to the rabbi’s house, but fled after he failed to gain access.

Lazer Klein, 19, who lives in the neighborhood, said he saw people “running away, screaming and calling the cops.”

“I saw someone lying on the stairs,” Klein added. “I saw people getting carried out. I saw blood. One guy was lying limp on the stretcher.”

Victims were transported to Westchester Medical Center and Montefiore Nyack Hospital, a source told The Post.

The incident is the latest in an area spate of violent incidents against the Orthodox Jewish community. So far during Hanukkah, eight anti-Semitic attacks have been reported in New York City.

The NYPD Counterterrorism Bureau tweeted that the incident is being monitored.

“I am horrified by the stabbing of multiple people at a synagogue in Rockland county tonight,” Gov. Cuomo tweeted.

“We have zero tolerance for anti-Semitism in NY and we will hold the attacker accountable to the fullest extent of the law,” he tweeted.

Tweeted Mayor de Blasio: “Horrific. So many Jewish families in our city have close ties to Monsey. We cannot overstate the fear people are feeling right now. I’ve spoken to longtime friends who, for the first time in their lives, are fearful to show outward signs of their Jewish faith.”

Dov Hikind, the former state assemblyman and founder of the Americans Against Antisemitism group, called the attack “Unbelievable.”

“It just doesn’t stop,” he said as he rushed north to the scene from the city.

“Between Jersey City and New York and now this — all of this hate is affecting people,” Hikind continued, “and giving sick people a license to attack Jews.”

Attorney General Letitia James tweeted: “I am deeply disturbed by the situation unfolding in Monsey, New York tonight.

“There is zero tolerance for acts of hate of any kind and we will continue to monitor this horrific situation. I stand with the Jewish community tonight and every night.”