Two fire engines from Ilfracombe were called to a pampas grass fire at Jubilee Gardens on Ilfracombe sea front at around 4.15pm on Sunday.
The fire service received a 999 call saying someone had let off a firework which had started a fire near the Landmark Theatre.
On route to the scene firefighters noticed that part of Jubilee Gardens was well alight.
Fire Incident Commander Mark Creek said: "When we arrived there was about 30 square metres of grass on fire and it was well alight.
"We're not sure exactly how it started but the report we had stated a firework had been let off in the area.
"It took us about 20 minutes to put the fire out with a hose reel from one of the engines."
A police spokesman said no offenders were identified at the scene and officers are appealing for anyone who witnessed any suspicious activity to get in touch.
Anyone with information can contact the police on 101 quoting log number 619 of December 9.