You said it started under or around the gas tank? I have seen several posts like this and it just happened to me. Not a fire though. I hopped a curb with my walk behind the the gas line fell out of the bottom of the gas tank. The rubber piece that holds the valve in cracks and leaks.
All equipment is wore out.
<- Never mind. All equipment has been repainted and with new decals. It's like I have new mower's again!
48" Ferris WB
36" Ferris WB
All Echo hand helds
<- That's how I feel at the end of the day.