An unknown explosive device went off inside a mailbox on Tuesday night in La Cañada Flintridge, causing minor damage to a vehicle and destroying the mailbox, authorities said.

The explosion occurred in the 300 block of Noren Street, just north of Crown Avenue, around 8 p.m., said Lt. Angela Shepherd of the Crescenta Valley Sheriff’s Station.

It’s unknown why the explosive device was set up inside the mailbox, she said. The incident is under investigation.

-- Tiffany Kelly,

Follow on Google+ and on Twitter: @LATiffanyKelly.