Tower Controller reported local controller created conflict in traffic pattern which resulted in a NMAC.

Narrative

I was working ground and was keeping an eye on the aircraft to help Local out. We had multiple Aircraft X's in the pattern and the Aircraft Y was inbound to land. Aircraft X's were on the left downwind while the Aircraft Y was on the right downwind. Aircraft X was on about a 4 mile final for Runway XX descending from 2000 ft. to 1500 ft. when the local controller said to make a right 270 turn. Aircraft Y was on the right downwind past the approach end of Runway XX at 1500 ft. The controller instructed Aircraft Y to start their right base right after instructing Aircraft X to turn right. Both aircraft were pointed at each other at the same altitude. The only words I was able to get out was 'what are you doing?' No traffic calls or wake turbulence calls were made by the local controller. Aircraft X was able to see the situation and pull up to 2000 ft. to avoid and appeared to overfly Aircraft Y. It did appear that the targets merged and I was unable to tell how close the aircraft got. It was an unsafe situation with no need to try and push aircraft like that. Controllers need to know its ok to extend aircraft in the pattern so they will fit without incident.