Access bank account if account holder is not well

Hello,

My father had road accident last year & he is still under coma stage.

My father is government employee in India & he received his monthly salary in his bank account.

Since he is in coma, he cannot speak, write or even sign on cheque book.

Since bank account is 25 years old & there was no procedure for nominee at that time.

We need to access his bank account to withdraw some money but without his signature we cannot withdraw money.

What i should do?

Aftaab