In case of any great emergency, the board may, by resolution passed by a four-fifths vote of all the members of a five-ward district, or by a five-sevenths vote of all the members of a seven-ward district, declare and determine that such emergency exists, and thereupon proceed to expend sums or enter into contracts involving the expenditure of any sums needed in such emergency without observance of the provisions requiring contracts, bids, or notice.