A woman has been arrested after the apparent stabbing death of a baby girl in Melbourne's north.

A family member called police to the house on Fordham Road in Reservoir about 11am on Monday.

Officers arrived to find the 13-month-old girl already dead, with what appeared to be stab wounds, a police spokeswoman said.

A 28-year-old Reservoir woman was taken into custody and is now assisting police with inquiries.