The city manager shall be the chief administrative officer of the city. He shall be chosen by the council solely on the basis of his training, experience, and administrative qualifications. The choice shall not be limited to inhabitants of the city or state, but the person chosen shall be a citizen of the United States. The city manager shall be appointed for an indefinite period, and he shall be removable by the council at any time. If removed at any time after one year of service he may demand written charges and a public hearing on the same before the council prior to the date on which his final removal shall take effect, but pending and during such hearing the council may suspend him from office. During the suspension, absence, or disability of the city manager the duties of his office shall be performed by some properly qualified person designated by the council.