It shouldn't be allowed but i've heard individual cases when this has happened. On one hand, the government should restrict this because otherwise people would just come in the country using visit visa and then stay here forever. On the contrary, if these people get to find a job where the company would offer sponsorship, then whatever they are making will be subject to tax withholding, then it will be ok.

I dont' think that's the intention of the 'visit visa'. If you want to work here and stay here, then you need to first try to get working visa.