Inside the nearly 800-square-foot building were 144 people, 70 of them fell into the basement.
"There was a partial floor collapse just at the start of the ceremony, and the people fell down into the basement," New Hampshire State Fire Marshal Sean Toomey said. "It was a walkout basement in that area. So, there's an initial report that people were trapped."
The fall was about eight feet, according to the state fire marshal.
Originally six people were taken to hospitals, four have since been discharged.
Other patients may have taken their personal vehicles.
The wedding ceremony was held in a building called the Sap House at The Preserve at Chocorua in Tamworth.
It's an old building that is known for hosting ceremonies.
"It looks like, preliminarily, that there's probably overloading situation in the structure. There's more people in there that probably should have been in," Toomey said.