PHILADELPHIA -- Authorities say a 6-year-old boy has been stabbed to death inside his New Jersey home, and his 12-year-old sister has been critically hurt.

The stabbings happened early Sunday in Camden, a city across the river from Philadelphia that continually ranks as one of the nation's most dangerous.

Police tell WPVI-TV (bit.ly/T64SBU) that an unknown assailant slit the girl's throat, and she went door to door to get help. A neighbor called 911.

The children were taken to a hospital, where the boy was pronounced dead. His sister is in critical condition.

The station reports that a 17-year-old had been baby-sitting the children because their mother was in the hospital. The teen wasn't hurt.

Police dogs are searching for clues. No arrests have been made yet.

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