A bomb explosion ripped through a passenger bus going to Noshki from Mastung earlier today, Aaj News reported.

The blast occurred when the bus was near Drangar area close to Quetta, earlier this morning.

At least four casualties are reported as of now while 50 people have been injured. Death toll is feared to rise.

The  injured passengers have been dispatched to the nearest hospitals, some in critical condition.

It is yet unclear if the bomb was planted in the bus or on the  road. Police has cordoned off the area for further investigation.