Nima Gajjar, spokeswoman for the group, said some fell over as they struggled to get out.
She said: "We were nearing the end of lunch and that was when it happened. My friend's daughter came up to me and said there was a gas leak.
"The moment she said it I got up, went towards the kitchen area and could smell gas.
"As soon as I smelled it I told everyone to move. As I was there it sounded like a gush of wind.
"As the gush came I remember shouting out 'Run, run', and we got them out.
"We were picking up each other's kids. I had my son, someone else had my daughter, and as we just got out it exploded.
"We were lucky, so lucky."
Incident commander Bill Smith, of Leicestershire Fire and Rescue Service, said: "Most of the guests were in and around a marquee area just outside the building. In the kitchen they had a large LPG (liquefied petroleum gas) cylinder hooked up to a large gas ring.
"After the meal they disconnected the pipe from the cylinder but the cylinder kept leaking.
"The person who disconnected the cylinder realised the danger of the gas leaking. He ran out and got everybody to run over to the other side of the road.
"Within 30 seconds there was a large explosion. He has no doubt saved the lives of many people with his actions."
When emergency services arrived it was unclear whether anyone was trapped inside, or underneath rubble left by the blast.
Firefighters searched inside the building, but had to withdraw when it became too unstable.
A search and rescue dog was also brought in.
Mr Smith said: "It's an absolute miracle that nobody's been injured or killed. You could tell how close people were because within about 10ft of the building were barbecue tables with food on."
East Midlands Ambulance Service said four people, including a firefighter, were treated at the scene for minor injuries.
Dillon Kidger, who works for a nearby roofing company, said he rushed outside after hearing a large explosion.
He said: "It was actually that loud that the building shook. I heard banging noises and people screaming, there was a big fire and the building was gone in about five to 10 minutes.
"I saw a few people praying outside and people walking round with cuts to their hands and faces from the shrapnel."
3rd September 2010, 7:44pm
The blast rocked the building after cylinders of gas powering a large cooker leaked during a festive meal.
