I would have to ask how is this child's language and communication level? They estimate that almost 90% of toddlers hit. They lack the communication and language to express their frustration so they hit. I would try to find out why he is hitting and work on that. Is something frustrating or upsetting him? Can you support him in that way and teach him other ways to deal with his frustration? If we terminated all children that "hit" our homes might become revolving doors????
If his language and communication is top notch then he needs to learn boundaries and limitations in your home. This is unacceptable behaviour and the instant it happens there is a consequence (time out) and it is very matter of fact. Stay calm and let him see that there are consequences to his actions (cause and affect) and do so every single time. My guess is that it won't take him long to learn :-)