In addition to the powers herein enumerated, the legislature shall have all powers necessary to the legislature of a free state, including the power to enact reasonable and appropriate laws to guarantee the continuity and effective operation of state and local government by providing emergency procedure for use only during periods of disaster emergency. A disaster emergency is defined as a period when damage or injury to persons or property in this state, caused by enemy attack, is of such magnitude that a state of martial law is declared to exist in the state, and a disaster emergency is declared by the chief executive officer of the United States and the chief executive officer of this state, and the legislature has not declared by joint resolution that the disaster emergency is ended. Upon the declaration of a disaster emergency the chief executive of the state shall within seven days call a special session of the legislature which shall remain in continuous session during the disaster emergency, and may recess from time to time for [not] more than three days. (As amended November 8, 1960.)