MINNEAPOLIS -- A construction worker plunged about 50 feet to his death at the Minnesota Vikings' new stadium site Wednesday morning, while a second worker with him was seriously injured.

Officials were still trying to determine how the accident happened, said John Wood, senior vice president with Mortenson Construction, the general contractor overseeing the $1 billion-plus project. Jeramie Gruber, an employee of Berwald Roofing Co., fell from the edge of the roof into a snow gutter on the north side of U.S. Bank Stadium about 45 minutes into his shift and was pronounced dead on arrival at a nearby hospital, Wood said.

Another man from the same subcontractor was injured on the roof but did not fall from it, Wood said, adding that the circumstances of how he got hurt also weren't immediately known. He also said he didn't know the extent of that worker's injuries. Wood said investigators were still determining what kind of work the two men were doing, whether they were wearing harnesses or other safety gear at the time, or whether such equipment was required where the men were working.

"This is a very tragic day in the life of the stadium construction project," Wood said at a news conference.

A woman who answered the phone at Berwald Roofing said nobody was available to comment.

Records showed that the company had received nine citations for serious safety violations at its worksites in the past five years -- many for workers failing to use safety harnesses.

Operations were suspended for Wednesday, leaving huge cranes standing idle over the site of the former Metrodome on the eastern edge of downtown Minneapolis. About 1,200 men and women work on the project, and they all held "a very somber gathering" after the accident, Wood said.

Work on the stadium resumed Thursday. Wood said counselors would be on site and will stay as long as necessary.

In a statement, the Vikings called the accident "extremely sad" and offered thoughts and prayers for Gruber's family, as well as for the injured man who remained hospitalized and all the other construction workers affected by the accident.

Wood promised "a very thorough investigation" and said Mortenson is cooperating with regulators.

"Our priority is to ensure that we know exactly what happened and ensure that it never happens again. A man lost his life on this project today and that simply never should happen," he said.

And while the project faces tight deadlines so the stadium can open in time for the Vikings' preseason in August 2016, Wood said that wasn't his concern now.

"We're not thinking about the construction schedule right now," he said. "We're thinking about these two men and their families."