A mother and her five-year-old son have been found dead in an apparent murder-suicide after a long custody battle with the boy's father.

The bodies of Gina Summers, 46, and her child Jude were found at their home in Orono, Minnesota in the US on Monday.

Police were alerted to a problem when father Jeff Sandberg, who had joint custody, tried to contact them to arrange to pick Jude up.

A typed and signed note believed to be written by Ms Summers was found in the home and detailed the "issues with the system and allowing a child to be ripped from his mother," The Star Tribune reported.

According to police, the note ended with: “Don’t let this happen to another child and mother.”

On Thursday, Mr Sandberg released a statement through his lawyer saying he is now planning a funeral for his son, a week after spending a family fishing trip with him.

"He was getting ready for his first day of Ready Start Kindergarten,” the statement said.

Mr Sandberg hit back at the allegations in the note, saying Ms Summers "refused to participate in ordered mediation."

According to court documents, Mr Sandberg and Ms Summers started a relationship in 2008 and had Jude four years later.

AFP