The gunman then apparently shot and killed himself, said Daniel Tushaus, chief of the Brookfield Police Department.
"There is nobody else being sought at this time as a suspect," he said.
Seven to eight people, ranging from their early teens to their 60s, were taken to hospitals in serious condition, he said.
The shooting was reported to police shortly before 1 p.m. Tushaus said it occurred during a regularly scheduled church service at the Sheraton hotel.
Some guests remained locked in their rooms after police surrounded the building and would not allow anyone to enter or leave.
Karen Suick, 48, said she arrived at the hotel Friday night with 15 players and parents for a hockey tournament.
"One of our hockey dad's two daughters are still in there," she said. "They called his cell phone. They were OK, but they were told to go back to their room. So that's what they did."
At least two church groups were holding meetings in the hotel at the time of the shootings, police said.
Brookfield is a western suburb of Milwaukee.