WHITCHURCH-STOUFFVILLE, Ont. - One man is in critical condition and three others are in stable condition in hospital after being struck by lightning at a golf course north of Toronto.

York Regional Police say the incident happened just before noon Tuesday at Bethesda Grange Golf Course in Whitchurch-Stouffville.

Witnesses at the golf course say they heard a horn warning them to get off the course and shortly afterwards heard a loud crack, believed to be the lightning.

Some of those at the scene rushed to assist the injured golfers by giving them first aid and CPR.

Police say a 51-year-old man from Thornhill, and two Toronto men -- aged 53 and 56 -- are in stable condition, while a 60-year-old-man from Richmond Hill is in critical condition.

Peter Epstein, one of the first people to reach the injured, says one of the men had no vital signs but was revived by an ICU nurse who happened to be playing golf, and a firefighter who arrived.