You really need to shut it down NOW.
First, check the oil to see if its overfull and/or milky.
True white smoke, especially if its sweet smelling, is antifreeze. Probably from a head gasket if you are lucky.
Small amounts getting into the cylinder is survivable. Probably no damage if you don't drive it much and get the gaskets fixed.
But, if its getting into the oil, then you can ruin bearings fast.
Bluish white smoke is oil burning, and will smell like.....Well burning oil.
In that case, it is even more important to check the oil.
If its a carb engine, don't remember right off the top of my head when they switched to fuel injected, then you could have gas getting pumped into your engine.
If so, then the oil will smell like gas. This will ruin bearings quickly.
If its FI, or the oil is low instead of high or smelling like gas, then you are quite possibly looking at a rebuild.
But, there are other tests to be made first.