A spectator died while at the U.S. Open at Erin Hills on Friday, the United States Golf Association announced.

The USGA did not provide any additional information on the death.

A statement from the organisation read: "The USGA was saddened to learn that a spectator at Erin Hills passed away a short time ago.

"Out of respect for the family, we are unable to provide additional information at this time. Our thoughts and prayers are with those surrounding this individual during this difficult time." 

WITI television in Milwaukee reported that the local medical examiner was called to the course on Friday afternoon after a man died of "natural causes."

The heat index at the course was in the low 90s as second-round play continued under sunny skies.