According to West Sussex Fire and Rescue Service, crews were called out just after 2am to reports of several beach huts alight on Marine Parade, Worthing.
In a post on social media, Worthing Fire Station, which sent two fire engines to the scene, wrote: "Upon arrival, three huts were fully involved in fire and rapidly spreading to adjacent ones.
"Crews wore breathing apparatus to deal with it. It was caused by someone deliberately setting fire to a motorbike behind them. The police and [Worthing Borough Council] are dealing with."
When approached for comment a county fire service spokesman said five beach huts and one motorbike was damaged by fire. It confirmed the Worthing Beach Office was also involved in the investigation.