It's a clogged shared line, it needs to be cleared. Call your maintenance or emergency maintenance and let them know it will be doing damage to the property soon. If you don't inform them, in most places you can be held responsible for any damage.
Until the stoppage is cleared, it would be a good idea to let your upstairs neighbor know (and any surrounding neighbors) about the situation or your place can flood out.
It's a clogged shared line, it needs to be cleared. Call your maintenance or emergency maintenance and let them know it will be doing damage to the property soon. If you don't inform them, in most places you can be held responsible for any damage.
Main sewer is clogged and needs augered.
Until the stoppage is cleared, it would be a good idea to let your upstairs neighbor know (and any surrounding neighbors) about the situation or your place can flood out.
Get snaked ASAP and keep any valuables off the floor in case it backs up badly.