All Los Angeles area public schools were shut down Tuesday after a number of school board members received an emailed threat that raised fears of a deadly attack like the recent mass shooting in nearby San Bernardino.

District has 640,000 students from kindergarten through high school 2:44

New York City officials said they received the same threat but quickly concluded it was a hoax. New York police Commissioner William Bratton said he thought Los Angeles officials overreacted, and New York Mayor Bill de Blasio told reporters he was "absolutely convinced" there was no danger to schoolchildren in his city.

"There was nothing credible about the threat. It was so outlandish," de Blasio said.

At a press conference Tuesday, Los Angeles police Chief Charlie Beck said it is easy to criticize in hindsight.

​"It's irresponsible to criticize that decision based on facts that have yet to be determined," Beck said. "All of us make tough choices. All of us want to keep our kids safe."

Los Angeles officials announced Tuesday evening that schools would reopen Wednesday.

A police officer puts up yellow tape outside of Edward Roybal High School. Police said the threat referenced explosives, assault rifles and machine pistols and specifically named schools in the Los Angeles Unified School District. (Richard Vogel/Associated Press)

Beck said the emailed message, which was brought to police attention late Monday night, threatened violence and included references to explosive devices, assault rifles and machine pistols.

The message, which specifically referred to all of the schools of the Los Angeles Unified School District, was routed through an IP address in Frankfurt, Germany. Police have yet to determine its origin, but Beck said authorities believe it was "much closer than Germany."

Beck said the L.A. police worked with the FBI to vet the message "as best as possible."

In New York, Bratton said the person who wrote the note claimed to be a jihadist but made errors that made it clear the person was a prankster, including spelling the word "Allah" with a lowercase "a."

Bratton added it looked like the sender of the threat watched a lot of the television drama Homeland.

A law enforcement official with access to the document provided the email to The Associated Press. The official was not authorized to disclose details of an ongoing investigation and provided it only on condition of anonymity.

The anonymous writer claimed to be a student at a district high school who had been bullied. In addition to misspelling the word "Allah, the message contained no reference to the Qur'an.

The threats came in simultaneously to New York and LA school officials at about 1:20 a.m. EST Tuesday, or about 10:20 p.m. Monday in Los Angeles.

Mayor supports school district

The shutdown abruptly closed more than 1,000 schools attended by 640,000 students across Los Angeles, and some private schools also followed suit. The city's police chief and mayor both said they support the school superintendent's decision to implement a system-wide shutdown.

"The decision was not mine to make, but it is mine to support as mayor of Los Angeles," said Eric Garcetti.

Beck echoed his words and said the the school district "safeguards three-quarters of a million lives every day," so when it takes a decision, it affects all of those lives.

Los Angeles police Chief Charlie Beck, centre, and Los Angeles Mayor Eric Garcetti, right, defended the decision to shut down the second largest school district in the U.S. due to an emailed threat. (Nick Ut/Associated Press)

"Southern California has been through a lot in recent weeks — should we risk putting our children through the same?" Beck asked, referring to the attack at a holiday party being held at a social services centre in San Bernardino that left 14 people dead.

Superintendent Ramon Cortines said the precautions the school board was taking were being done in "a calming way." He said students would not return to class until every campus had been searched and he had received a report from the school board certifying that they are safe.

Lupita Vela, who has a daughter in elementary school and a son in high school, called the threat "absolutely terrifying" in light of the San Bernardino attack.

She got an automated phone call informing her of the closure.

"I know the kids are anxious," she said.

'It was many schools'

The Los Angeles Unified School District, which takes in Los Angeles but also several other independent municipalities and unincorporated areas, commonly gets threats, but Cortines called this one rare.

"It was not to one school, two schools or three schools," he said at a news conference. "It was many schools, not specifically identified. But there were many schools. That's the reason I took the action that I did.… It was to students at schools."

The San Bernardino attack influenced the decision to close the entire district, Cortines said.

Students stand out front of Venice High School in Los Angeles. (Jonathan Alcorn/Reuters)

The superintendent said the district police chief informed him about the threat shortly after 5 a.m.

"He shared with me that some of the details talked about backpacks, talked about other packages," Cortines said.

Vela said she worries about talking to her kids about the threat and terrorism in general. She's concerned about her daughter feeling safe in class.

"I don't want this to be in the back of her head," she said. "Who knows what it does psychologically to kids? Is this going to cause her some kind of trauma so that she's not going to feel safe at school?"

Ranking Democrat on the House intelligence committee Adam Schiff, and other federal officials, said the threats sent to school boards in New York and Los Angeles were most likely a hoax. (Alex Wong/Getty Images)

The threat that closed down all public schools in Los Angeles is most likely a hoax, said Adam Schiff, ranking Democrat on the House intelligence committee.

Several federal officials, who asked not to be named, echoed an assessment by Bratton that the decision Los Angeles authorities took was an over-reaction.

Earlier, White House spokesman Josh Earnest said he would not second-guess the decisions made in Los Angeles or New York.