Six construction workers were hospitalized Wednesday — two with serious injuries — when a large structure they were building in Conestoga Township collapsed, police said.

Sixteen employees of King Construction were inside a 90-by-220- foot structure on Kirk Liddell's farm in the 100 block of River Hill Road when several large roof trusses collapsed about 12:30 p.m., police said.

The workers, all males, were setting the trusses for a new indoor horse-riding arena, Liddell, a prominent Lancaster businessman, said.

Twelve workers were on the trusses and the other four were on the ground when the structure toppled, according to Southern Regional police Officer John Michener.

None of the workers was identified Wednesday.

A local building inspector and engineers from King Construction of New Holland were trying to determine the cause of the accident Wednesday evening.

"At this point, it's a mystery," Liddell said. "They are very experienced and respected builders of horse buildings like this. We are not aware of anything not done properly."

Six of the workers were hospitalized while the others were either treated at the scene or uninjured, police said.

Two of the workers were taken to Lancaster General Hospital's trauma unit. They both had leg fractures and lacerations and were complaining of back and chest pain, Michener said.

One of those men was working on top of one of the trusses when they fell, Michener said. Both of the man's legs have compound fractures, Michener said.

The other man taken to Lancaster General's trauma unit was in surgery Wednesday night and is expected to remain hospitalized for a few more days.

The workers began setting trusses Wednesday morning and had half of them in place when "something happened," Liddell said.

"All of a sudden, it just went. There was little or no warning," Liddell said.

Liddell is chairman, president and chief executive officer of Irex Corp., which provides new construction and maintenance services to business clients in the United States and Canada.

Most of the trusses fell about 20 feet to the ground, police said.

"It was kind of like dominos," Liddell said. "One went down, and started bumping against the next."

One man who was on the ground escaped injury when he ducked for cover into an open space between the trusses, Liddell said.

"He thought about running for it, but then he hit the ground and that saved him," Liddell said. "He was under the trusses, but they created a little umbrella over him."

Construction on the horse arena started last week.

"It was just coming up off the ground," Liddell said.

Liddell credited first-responders for a fast arrival.

E-mail: bhambright@lnpnews.com