Accidents in which limbs are completely severed are mercifully rare.
Get the casualty to lie down raise the affected limb, and tie a bandage rightly around and over the stump. If the wound continues to bleed, add another bandage, applying as much pressure as you can. Put the severed limb in a clean container or plastic bag, and if possible pack the container with ice. Watch carefully for symptoms of Shock. Take the casualty and the amputated limb to the nearest hospital as quickly as possible. Make sure the staff know that the severed part has come with the casualty.