Sounds like the crankshaft oil seal has failed, with it being concealed by the belt cover it may have been seeping for some while un-noticed and has now failed completely.
Risky to have continued driving it as the oil may have contaminated the cam belt as well as oil starvation, just hope there is no further engine damage as a result.
I certainly wouldn't risk even cranking the engine without stripping it down and finding the cause, if the belt snaps the engine would certainly be as good as scrap.