The derailment of a train carrying crude oil from North Dakota through West Virginia is another sign of the need to address safety, a federal regulator said.

The National Transportation Safety Board estimated 28 tank cars of the 109 from a CSX line slipped the rails early Monday afternoon near Mt. Carbon, W. Va.

The state Department of Military Affairs & Public Safety estimated that about a dozen of the cars were carrying crude oil, which would equate to approximately 8,000 barrels. The NTSB said an undetermined amount of crude oil spilled into an area river.

U.S. crude oil production levels are more than the existing pipeline infrastructure can handle, forcing energy companies to use rail as an alternative transit method. The increase in crude oil transport by rail has raised safety concerns, most notably in the wake of a deadly 2013 accident in Lac-Megantic, Quebec.

Most rail incidents involving crude oil spills were tied to cars labeled DOT-111. The incident in West Virginia involved newer model cars designated CPC 1232.

"This accident is another reminder of the need to improve the safety of transporting hazardous materials by rail," NTSB Acting Chairman Christopher Hart said in a statement Tuesday.

The NTSB said it has a team on the ground working alongside local, state and federal officials, as well as those from CSX, to review the events leading up to the incident. The federal safety agency said investigators are comparing data on tank car designs to similar U.S. derailments in 2013 and 2014.

West Virginia Gov. Earl Ray Tomblin declared a state of emergency for the areas in and around the derailment. At least one home was destroyed, minor injuries were reported and water supplies were disrupted as a result.

The cause of the derailment is under investigation.