A rural county bridge in central Missouri collapsed when a semi-trailer truck tried to cross it despite the bridge's 5-ton weight limit, authorities said.

WESTPHALIA — A rural county bridge in central Missouri collapsed when a semi-trailer truck tried to cross it despite the bridge's 5-ton weight limit, authorities said.

The truck driver escaped injury when the Pentecostal Bridge collapsed Monday morning where it crosses the Maries River near Westphalia, Osage County Sheriff Michael Bonham said. 

The bridge's 5-ton weight limit is displayed on signs, Bonham said. The average 18-wheeler weighs close to 40 tons, according to website The Truckers Report.

Bonham said his office is trying to determine why the large truck was in the area, The Jefferson City News-Tribune reported.

"That's a gravel road, where he was at, and we're not sure why he was over there," Bonham said. "It's a very light weight limit. There's no way a tractor-trailer should be over there or on that bridge at all."

The Missouri Highway Patrol also will investigate the incident.