The family of a young man who went on a deadly shooting rampage in two Colorado religious centres before killing himself said they were "groping for answers" and praying for the victims' families.

Authorities searched a home in the US state of Colorado early today, seeking any link between two deadly shooting sprees at Christian religious centres that left both communities baffled and stunned.

A gunman killed two members of staff at a US missionary training centre after being told he could not spend the night there.

A gunman walked into a training centre for young Christian missionaries in a Denver suburb in the US early today and opened fire, wounding at least four people.