A 4-year-old was sleeping in the mobile home struck by a cannonball that killed a 33-year-old woman in San Diego County, officials said.

The incident, which is being investigated by the San Diego County Sheriff's Department, took place when the woman's husband and another man were working on a cannon shortly after midnight outside the couple's mobile home and it exploded, according to a Cal-Fire spokesman.

One of the two men was sent to a hospital with minor injuries, but the 4-year-old was not hurt, officials said. A Cal-Fire spokeswoman said the woman's husband was "freaking out" after the incident.

Authorities said the cannonball was homemade and that alcohol was involved. The mobile home was located near rural Potrero in eastern San Diego County.

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-- Tony Perry in San Diego