People across the Northern California city of Woodland were woken up early Tuesday morning by a loud, mysterious boom that rattled windows, set off car alarms and left neighbors wondering what caused it.

A home security camera captured the strange sound and aftermath. In the video, you can hear it start with a whistle, followed by a flash of light and then a big boom.   

"I thought it was a bomb, actually," said Jennie Buse, who heard the loud noise. 

What the 5:20 a.m. wake-up call was is still a mystery to investigators with the Woodland Police Department.

"The first thing I thought was it was probably a home that exploded or something," said Pablo Cruz, who also heard the boom. 

Woodland police said they got multiple reports that someone may have shot something off in the sky, but when patrols went out to investigate, they found no damage, fires or evidence of an explosion. 

It said most of the reports were from the area of Ashley Avenue and Riverside Drive, on the west side of the city and just north of Main Street.

Cruz said he was even bracing for a second boom that never came. He went outside after the noise to see what was going on but did not find anything. 

"We looked and there was nothing after that, just the one big boom," Cruz said. 

Residents say they have never heard or seen anything like this. 

"It was kind of scary," said Buse. "It kind of threw me off." 

Police said that at this point, they cannot determine what caused it. No injuries were reported.