Los Angeles schools have been closed as an unspecified threat emailed to the school district is being investigated.
The threat against the second largest school system in the country led to students being told to stay at home and school buses being returned to depots.
A school district spokesman said it involved rucksacks, and they were exercising "an abundance of caution".
New York City officials said they received the same threat that closed LA schools but concluded it was a hoax.
Police are searching all the schools, which will remain closed until the threat is over, officers told reporters at a press conference.
Source:
http://www.bbc.com/news/world-us-canada-35102954