If you find this in your house, where the house wiring runs from 120 to 240Vac, grab anything non-conductive and GET IT OFF THE WIRE!
Fractions of a second number! Plastic, wood, or rubber. You should not touch them directly and avoid touching them with any conductive material.
Have a rope? You can wrap it around your hands and pull like mad! The same can be done with a tarp. Pull hard! Act quickly! You could be literally frying their skin if you wait. DO NOT TOUCH THEM.
If they won’t let go of the wire and you’re wearing rubber soled shoes with rubber soles, kick them out. It’s better to have a broken arm than to be dead.
An extension cord has no conductivity on the outside. It can be used as a rope.
If it’s elsewhere, STOP THE BREAKER. Do not do anything else. Even a branch, rope or 2×4 can become conductive enough to cause electrocution at higher voltages.
If you do not have access to a circuit breaker, such as a downed powerline, DO NOT GO! Tell 911 what’s happening and where you are. They cannot be moved, and you can’t move the wire without risk because you don’t know what the voltage is. Conduction along the ground can cause shock, especially if it is wet.
I’m not a doctor or an electrician.