(2) Whenever, owing to any sudden change in the channel of any navigable river or other unforeseen emergency, it becomes necessary for any Railway Administration to acquire the immediate possession of any land for the maintenance of their traffic or for the purpose of making thereon a river side or that station, or of providing convenient connection with or access to any such station, the Collector may, immediately after the publication of the notice mentioned in sub section (1) and with the previous sanction of the appropriate Government, enter upon and take possession of such land, which shall thereupon vest absolutely in the Government free from all encumbrances: Provided that the Collector shall not take possession of any building or part of a building under this sub section without giving to the occupier thereof at least forty eight hours ' notice of his intention so to do or such longer notice as may be reasonably sufficient to enable such occupier to remove his movable property from such building without unnecessary inconvenience.