At least five people have been stabbed at the house of a rabbi in New York state, police say.
The house in Monsey, north of New York City, was hosting a religious celebration when the attacker burst in, according to the Orthodox Jewish Public Affairs Council (OJPAC).
The suspect fled but was later taken into custody, police said. The motive was not immediately clear.
One of the victims was stabbed at least six times, OJPAC said in a tweet.
The attack came a day after New York city police said officers were stepping up patrols in heavily Jewish districts following a spate of anti-Semitic threats and attacks.
A man brandishing a machete attacked a Hanukkah celebration at the rabbi's property in Monsey - an area with a large population of ultra-Orthodox Jews, CBS New York reported. The incident happened at about 22:00 on Saturday (03:00 GMT Sunday).
"The house had many dozens of people in there," Yossi Gestetner, a co-founder of OJPAC for the Hudson Valley region, told the New York Times.
Aron Kohn, 65, was in the rabbi's home at the time. He told the paper: "I was praying for my life. He started attacking people right away as soon as he came in the door. We didn't have time to react at all."
Mr Kohn said that the attacker then tried to enter a synagogue next to the house, but people inside had locked the door.
Reports said the attacker fled the scene in a car and some witnesses noted the number plate. Police said later they had located a matching vehicle and arrested a suspect.
What reaction has there been?
New York Governor Andrew Cuomo said the stabbings were a "despicable and cowardly act".
"Anti-Semitism and bigotry of any kind are repugnant to our values of inclusion and diversity and we have absolutely zero tolerance for such acts of hate," he said in a statement.
Letitia James, the New York Attorney General, said she was "deeply disturbed" by the situation.
"There is zero tolerance for acts of hate of any kind and we will continue to monitor this horrific situation," she said in a Twitter post.
The New York Police counter-terrorism unit said it was "closely monitoring" the reports.
We are closely monitoring the reports of multiple people stabbed at a synagogue in Monsey, NY (Rockland County) pic.twitter.com/cHoQnbneKO— NYPDCounterterrorism (@NYPDCT) December 29, 2019
In Israel, President Reuven Rivlin expressed his "shock and outrage" at the attack.
"The rise of anti-Semitism is not just a Jewish problem, and certainly not just the State of Israel's problem," he said in a statement.
"We must work together to confront this evil, which is raising its head again and is a genuine threat around the world."
The attack follows a series of anti-Semitic threats and attacks in and around New York City. On Friday Mayor Bill de Blasio announced extra police patrols in three areas of Brooklyn.
Responding to the attack in Monsey, Mr de Blasio said he could not "overstate the fear people are feeling right now".
"We will not allow this to become the new normal. We'll use every tool we have to stop these attacks once and for all," he said.
I am deeply disturbed by the situation unfolding in Monsey, New York tonight.— NY AG James (@NewYorkStateAG) December 29, 2019
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.
The Jewish holiday of Hanukkah marks the victory of Judah Maccabee over the Syrian Greeks in the Second Century BC and the recapture of Jerusalem.
Are anti-Semitic attacks on the rise in the US?
On Friday New York city police's hate crimes unit said it was investigating eight anti-Semitic incidents reported since 13 December.
They included a threat by a man who walked into an Orthodox Jewish community organisation's headquarters in Brooklyn and threatened to shoot someone. In another incident a 30-year-old woman reportedly slapped three women in the face.
New York Police Department commissioner Dermot Shea has said hate crimes in New York City are up 22% this year.
"You see a swastika being drawn, you see a brick being thrown through a window, you see a woman walking down the street with her kids and having her wig ripped off," he said.
Earlier this month officials in New Jersey said a gun attack that killed a detective and three people in a Jewish supermarket was being investigated as "potential acts of domestic terror, fuelled both by anti-Semitism and anti-law enforcement beliefs".
In April a gunman killed a female rabbi and wounded three people at a synagogue in San Diego.
That attack came exactly six months after the deadliest anti-Semitic attack in US history, when a gunman killed 11 worshippers at the Tree of Life synagogue in Pittsburgh.