What will be the immediate action by the pilot and ATC if any plane blocks the runway while landing?
ATC will tell the landing plane to go-around. The pilot will then execute the go-around by flying the missed approach procedure as published in the airport charts.
Go-arounds happen daily and are pretty much a routine action.  

In any case, if the landing pilot feels that the runway is not safe for landing, he can decide to go-around by himself without ATC order (if the controller missed the issue or if the airport is uncontrolled for example).



For reference, the missed approach procedure can be as simple as:  


Stopping descent
Climbing back to a published altitude
Flying a published pattern 
Trying a second approach