Thanks for your suggestions.
What if the top layer of concrete is removed first upto the tile level and then lay the tiles again with sand (mitti) to make a proper slope so that water flows away during rain.
Another suggestion was made to first do as above but put marble on the top.
I'm just worried if the fault is with the lentel, cracks might appear again.. then what...
Third option might be to do chemical treatment. Not sure if the chemical can seal up this bigger gaps.