A woman who leapt 20ft from her burning home had to be taken to hospital after she slipped and landed on her head and back.

An explosion tore through six flats in King Edward Avenue, Worthing yesterday afternoon.

Schoolboy Billy Hilton ran into the smoke-filled building to alert people inside after hearing a “massive bang” as he cycled past with friend Natalie Mills at about 5.20pm.

Neighbours said one resident of the flats, thought to be owned by social housing firm Worthing Homes, was having a barbecue on his balcony, next to a gas boiler, when the explosion happened.

Two women were forced to jump from their burning flats' balconies after being trapped by smoke and flames. Eye-witnesses said the first woman “jumped out fine” but the second slipped and fell.

Billy, a 13-year-old pupil at Worthing High School, said: “I was riding on my bike and I heard the big bang and saw a load of smoke coming from the building.“I ran up to it and there was people shouting and coming out of the building. I ran inside and banged on the doors to try and get them out.

“I think I managed to knock on around eight doors but some people had to jump out the window. When I got downstairs I saw one of the people jump.

“She fell on her back and hit her head on the pavement. She was crying really badly.”

Natalie, eight, added: “We were cycling around the street and then we heard the big bang. It was scary and I was frightened, but then Billy went into the flats.

“I was screaming at him to get out because I was scared something would happen.”Billy's stepmother Amy Whybrow, 29, said: “He has asthma so he's lucky he didn't inhale too much smoke. It was brave.”

The Kent, Surrey and Sussex Air Ambulance landed in nearby Kitty's Field.

An eyewitness who lives next door to the building said the explosion was caused by a man who had a barbecue on his balcony.The woman, who wished to remain anonymous, said: “He was having it next to some kind of boiler and it exploded.

“It looked nasty because the first woman jumped out fine, but the second one looked like she slipped and fell. I think that's why the air ambulance came as she hurt her back quite badly.

“I hope she is going to be ok.”

Another neighbour said: "It was billowing out with thick black smoke. I didn't see flames, just smoke.

“The lady who owned the flat was pretty distraught. She has a little baby but they're being treated by the Redcross."

Fire crews, police, paramedics and the British Red Cross all arrived at the scene shortly after 5.30pm.

A volunteer for the Red Cross said: “We are here to make sure people are safe and have support.”

Engineers from Southern Gas Networks worked to make the scene safe yesterday evening. A spokeswoman from West Sussex Fire and Rescue said an investigation is being carried out to establish the cause of the fire.

She added: “One person was treated by South East Coast Ambulance for injuries at the scene and has been conveyed to hospital for further treatment.”