A 100-year-old man is believed to have murdered his wife with an axe as she slept before killing himself.

Bergen County prosecutor John Molinelli said there was a "history of domestic issues" between Michael Juskin and his 88-year-old wife Rosalia, but it was not clear what sparked the apparent murder-suicide in Elmwood Park, New Jersey, on Sunday night local time.

Police found the couple in their Spruce Street house after a relative, who was not in the home, called authorities.

Neighbours told The Record newspaper that they often saw the couple out and about - Michael Juskin walking a dog and his wife tending to her garden - but said they kept to themselves.

Barbara Szczecina, 65, said she saw Mrs Juskin sitting on her front porch at about 10am on Saturday.

"She used to be in her garden all the time," Ms Szczecina said. "They were always together, putzing around outside."

Family members declined to comment on the deaths.