BOSTON -- Four people remain in critical condition after a bolt of lightning struck 10 men watching a soccer game at Boston's Franklin Field Sunday afternoon.

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The men had taken cover under a tree at the edge of the soccer field near Talbot Avenue about 3:30 p.m. when a thunderstorm approached. A sudden bolt of lightning knocked them all unconscious.

"They all just dropped. Boom," one witness said.

All of the victims were males suffering burns consistent with lightning strikes. The youngest was 12 and the oldest was a man in his 40s. Boston police said two men suffered heart attacks and were taken to Boston Medical Center. The boy suffered burns and was admitted to Children's Hospital.

"They were all laying down, so it was a very terrible scene," another witness said.

Emergency workers administered CPR and all the victims were taken to area hospitals. All were expected to survive.

The sudden afternoon thunderstorm lit up the sky with lightning and drenched the Boston area, triggering street flooding in some places as nearly an inch of rain fell in less than an hour.

Officials said the victims were attending the Salvadoran soccer league’s regular Sunday game and if it had been called as soon as the rain started more people might have been huddled beneath the tree.

["The victims] sought the quickest shelter, but unfortunately, lightning strikes the tallest object, and that was the tallest tree in the area," Michael Bosse, an EMS deputy supervisor, said at a news conference at Boston Medical Center.

Bosse said in 27 years on the job he has never seen 10 people hit by lightning at once.

On average, about 400 people are struck by lightning every year, according to the National Weather Service. Most experts say to avoid standing under trees during lightning storms.