WEBBERS FALLS, Okla. ? A barge knocked out a 500-foot section of an interstate bridge over the Arkansas River on Sunday, sending at least nine vehicles plunging into the water and leaving at least half a dozen people trapped, authorities said.

Six cars and three tractor-trailers could be seen in the water, and dive teams were on the way to the scene, in the southwest part of the state, said Sgt. Jarrett Johnson of the Oklahoma Highway Patrol.

Six to 11 people remained trapped in submerged vehicles hours after the collapse, said Rebecca Smith with Muskogee County Emergency Management Services.

“We anticipate several fatalities,” Smith said. At least four people were being treated for injuries.

A second bridge where traffic would have tried to pass after the Interstate 40 bridge collapsed also was hit Sunday morning and was shaking but hadn’t collapsed, said Webbers Falls Mayor Jewell Horn. It wasn’t clear if the same barge hit both bridges. Horn said that bridge had since been closed.

The I-40 bridge collapsed at 7:48 a.m. during a severe thunderstorm, according to the Highway Patrol, but Horn said it wasn’t clear when the barge hit it. The collision could have happened before dawn and the bridge could have later collapsed under the weight of the vehicles, she said. She said the bridge was about 20 years old and 100 feet high.

Lake patrol units were interviewing the captain of the barge, Johnson said. Johnson said he did not know what caused the collision.

“There are probably thousands of cars that travel over this bridge every this day,” Johnson said. “It’s the main interstate that travels east and west through the state of Oklahoma.”

The bridge is about 100 miles east of Oklahoma City and about 35 miles west of the Arkansas state line.

The National Transportation Safety Board was sending a team to investigate.

At least four patients were being treated at Muskogee Medical Center, three in stable condition and one in critical condition, spokesman Chad Wetz said. He said one is a 62-year-old man, and two are in their 30s or 40s.

One patient told Wetz he only recalled the bridge collapsing and then waking up in the hospital.

“He said he was driving along, and the next thing he knows, there was no pavement under him, and that he was headed for a concrete pillar of some sort and hit the water,” Wetz said.