A CL65 flight crew experienced 'Fuel Imbalance' warning message soon after takeoff and again later in the climb. They ran the procedure and coordinated with company; electing to divert to the nearest suitable airport.

Narrative

After takeoff at approx 400 FT AGL we made a left turn to 310 degrees. During the turn master caution 'Fuel Imbalance' came on. Fuel imbalance was 900 LBS additional fuel in the left tank. After wings went level message went out and R AUTO Cross Flow pump came on. Then at 9;000 FT we were given a left turn to the southwest and same FUEL imbalance message came on; this time showing 1000 LBS heavy on the left side. Captain asked for the QRH for Fuel Imbalance and after the checklist was complete; Captain decided to divert and asked me to contact the company. Initially we had discussed Airport 1 for diversion; the company wanted Airport 2. We were approx in the middle of the two airports and we elected to go to Airport 2. An emergency was declared by the Captain and we were limited to very shallow bank turns to the left and normal turns to the right. We over flew Airport 2 heading east and made a right downwind entry for the runway. By that time the fuel imbalance was just about fixed by cross flow pump and made a normal landing; then proceeded to taxi under our own power to the gate. 3.5 hours later we had the passengers on a different airplane finishing our flight to our original destination.