It's been so hot in upstate New York recently that a pile of horse manure caught fire.

The state's department of environmental conservation says it received lots complaints about the smell.

The burning pile of horse muck was spotted at a property in the town of Throop, in the Finger Lakes region, 20 miles west of Syracuse.

The officer who was called said the owners of a horse stable had been storing the manure in large piles.

Apparently they've been spontaneously combusting in the heat and dry conditions.

State officials say a shift in the winds carried the odour of burning manure into the neighbours' windows.

It took three local fire departments two hours to douse the burning dung.

Temperatures this month have been hitting 32C (90F) in New York State.

America's National Fire Protection Association says spontaneous combustion is a by-product of spontaneous heating.

That happens when a material increases in temperature without drawing heat from its surroundings.

If the material reaches its ignition temperature, spontaneous ignition or combustion can happen.

Other materials which can spontaneously combust include oily rags, hay and other agricultural products.

So hay bales can catch fire inside a barn if they're wet or haven't been treated properly to begin with before being stored.

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