Urgent

no a company cannot appoint a auditor in middle of the year ...in case for that it needs prior permission of Central government or a spoecial resolution to be passed in the AGM ...or if not passed then they will have to wait till next AGM ...or if CG agrees with the reason given by company to withdraw the consent of the auditor then only auditor will have to leave/vacate the office of statutory auditor of the company .... 

Yes , Pl refer sec 224.

Provided that—

(a) the company may, at a general meeting, remove any such auditor or all or any of such auditors and appoint in his or their places any other person or persons who have been nominated for appointment by any member of the company and of whose nomination notice has been given to the members of the company not less than fourteen days before the date of the meeting; and

(b) if the Board fails to exercise its powers under this sub-section, the company in general meeting may appoint the first auditor or auditors.

(6) (a) The Board may fill any casual vacancy in the office of an auditor; but while any such vacancy continues, the remaining auditor or auditors, if any, may act:

Provided where such vacancy is caused by the resignation of an auditor, the vacancy shall only be filled by the company in general meeting.

(b) Any auditor appointed in a casual vacancy shall hold office until the conclusion of the next annual general meeting.

(7) Except as provided in the proviso to sub-section (5), any auditor appointed under this section may be removed from office before the expiry of his term only by the company in general meeting, after obtaining the previous approval of the Central Government in that behalf.

overall they have to take the permission of the Central government....

as per my knowledge,

company can appoint statutory auditor in the middle of the year...

company needs approval of central government and special resolution is also required to pass...

whats  the reason for removal of existing auditor? whether it is caused by casual vacancy or by disqualification of an auditor as specified u/s 226 (3), 226(4), 226(5)?

explain your reason, then i can explain you briefly..

agree with gaurav..

refer section 224, 225 and 226 of companies act