An explosion that disturbed residents in Hawaii Kai early Tuesday morning was likely an illegal firework, a fire department spokesman said.

Police said dispatchers received numerous calls about a loud explosion about 2:15 a.m. and firefighters were dispatched because it was thought to be a blown transformer. No damages were found and the exact cause was not determined, police said.

While investigating, firefighters spoke with a security guard in the area who saw aerial fireworks going off about the same time as the explosion, said Honolulu fire Capt. Terry Seelig.