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Investigators in the small southern Colorado town of Ordway are trying to figure out what caused a house explosion.

Three children, ages 3, 2 and 1 were inside at the time, along with their 21 year old babysitter. Family members say all are in critical condition.

The home exploded Tuesday. Investigators say it was so strong, it blew the doors 67 feet.

They are still looking for the cause of the blast. The natural gas company says the gas lines appear to be fine, so they don't think that was the cause.