Tournament favorite Tiger Woods hit only one shot before the horn sounded. He is playing in the same threesome with defending champion David Toms and British Open champion Ernie Els.
There was no rain falling when play was halted, but officials are being very cautious after what happened the last time Hazeltine National Golf Club hosted a major championship.
In the 1991 U.S. Open, spectator Billy Fadell was killed and five other were hospitalized when struck by lightning on June 13.
Scattered showers and lightning are expected throughout the week in Chaska, Minn.
With the delays, it is unlikely that everyone in the field of 156 will complete their first rounds Thursday.
The final group is now scheduled to tee off at 4:55 PM local time.
Full-field scores from the 84th PGA Championship