Plot purchase on as is where is basis

The purchaser of the vacant plot cannot be held liable for the mortgage loan dues that the owner has to pay to the bank, however if there is any mortgage loan  pending you may better ask the seller to clear the loan and then execute the registered sale deed or else you better do not venture into this risky investment  which may attract dispute or litigation at a later stage

You have stated, that, "........land parcel for internal road and amenity, open space is mortgaged to private individuals............" implies that title of the plot is defective (under mortgage).

It is better to seek professional opinion and advise of a local prudent lawyer with relevant land records for proper appreciation of facts.

There could be no meaningful suggestion unless the documents are perused and issues discussed.