To and towards: both are prepositions of movement
To : used if the destination is certain.
Here - certain destination is Mumbai (after that the journey will stop)
Toward: used if the destination is not certain, only the direction of something or someone where movement is taking place, is mentioned.
The child crawled towards the door.
Here, no certain destination is given just direction of movement I.e. 'door' is given. We don't know if the child will move any further or not.
Some more examples