Police were called to Mattel Inc.'s corporate headquarters in El Segundo on Tuesday after a plastic bottle exploded.
A security guard at the toy company's design studio at 2031 East Mariposa Ave. reported hearing what sounded like multiple explosions around 7 a.m., according to El Segundo police.
When authorities arrived, they found that a plastic bottle had exploded.
Employees inside were evacuated while sheriff's arson and explosives investigators inspected the facility, but nothing else was found.
Police say they believe it was a prank but are still investigating.
No injuries were reported.