The fire service confirmed that crews were called to a house fire in Pavilion Road at just after 9.10am today (Monday, June 12).
An ambulance was also in attendance.
Joe Bullington, watch manager at Worthing Fire Station, said: “When we turned up fire was already fully involved.”
Everyone was out of the property when the crew arrived, he said, and the street was smoke logged.
He believed the fire had started accidentally in the first floor bedroom before spreading to the roof.
Breathing apparatus and a hose reel was used by the crew to contain the fire, he said.
A male suffered burns to the leg and arm and three people were treated for smoke inhalation, according to Mr Bullington.
He also said volunteers from the Red Cross would be able to provide residents with support following the fire.
A fire service spokesperson confirmed that the first floor suffered 25 per cent damage, and the roof suffered 20 per cent damage.
The fire was put out by 10.23am.
Police said they were made aware of a building being ‘well alight’, but that West Sussex Fire and Rescue Service did not require police assistance.