The Authority may amend the whole or any part of the master plan, if necessary, at the expiry of every five years in accord ance with the procedure prescribed by the Act and these rules as if the proposed amendment were a new master plan:
Provided that if the Authority is of opinion that having regard to the circums tances prevailing at any particular time it is necessary so to do, it may amend the master plan or any oart thereof at any time prior to the expiry of"the said period, in accordance with the aforesaid procedure:
Provided further that the Authorliy m«v, without following the aforesaid proce dure but with the prior approval of the Central Government, permit, on receipt of an application in this behalf, any change (n the size of public parks and recrea tion grounds not exceeding ten peT cent, either way of the approved size.