The injuries were not life-threatening, an official said.
Pastor Tommy Davis at Freedom Baptist Church in Myrick told The Chronicle in Laurel that the floor at the activity center collapsed as dozens of youths held a worship service Wednesday evening. Witnesses described an ominous-sounding rumble before the floor crashed down.
"In the middle of the student service, the floor - which is a second-story floor - gave way, causing about 70 students to fall," Davis said. "But it's got to be said that no one was seriously injured, no one was trapped. God's hand was certainly taking care of the kids who were in that building."
Survivors reported brief moments of panic before calm was restored.
Linda Cranford, a spokeswoman for the Jones County Fire Council in the region where the church is located, told The Chronicle that 35 people were hurt but none of the injuries was life-threatening. She said a 16-year-old girl with a head injury was taken to a hospital in Hattiesburg.
She said 19 others were taken to a local hospital closer to the church. Authorities said most of those hurt were later released and witnesses described injuries including scrapes, cuts and possibly some broken bones. Several others were treated and released at the church grounds and didn't require further medical attention, reports said.
Cranford did not immediately answer calls from The Associated Press for comment early Thursday.
Students said the collapse came unexpectedly while the service was under way, starting with a rumble in the building. Tori Hodge, 18, told the newspaper there was an initial scene of panic before calm prevailed.
"We heard a huge rumble and the floor collapsed and people collapsed with it," she said. "Everbody heard it. The floor started crumbling and waving. People started falling through the ceiling, just like you'd see in a movie."
There was no immediate report on what caused the floor collapse.
Davis praised the leaders of the worship service for quick action in restoring calm. He said the students, in seventh to 12th grades, were all reunited with their parents afterward.
A number of the shaken students had only minor injuries and were treated and released at the scene once they were checked out by emergency crews, authorities said. Worried-looking relatives stood by amid the flashing lights of ambulances and emergency vehicles in the aftermath.
Jones County Sheriff Alex Hodge told local media outlets that the drop was about 12 feet in the floor collapse.
Dispatcher Amanda Lofton at the Jones County Sheriff's Office told The Associated Press early Thursday that she had no additional information to release about the injured and no information on a possible cause of the floor collapse.
Myrick is a small rural community northeast of Hattiesburg in southeastern Mississippi.