BETHLEHEM, Pa. — Norfolk Southern crews and contractors are working on cleanup and track repair after a collision and derailment in eastern Pennsylvania over the weekend involving three trains that left some railroad cars scattered along a riverbank and at least one partially in the river.

Officials in Northampton County said the derailment was reported at about 7:15 a.m. Saturday in Lower Saucon Township along the Lehigh River. Local authorities said no injuries were reported, no hazardous materials were involved and no evacuations were ordered.

The National Transportation Safety Board said preliminary information indicates an eastbound Norfolk Southern train struck a stopped Norfolk Southern train, sending wreckage onto an adjacent track that was hit by a westbound Norfolk Southern train. Cars from two of the trains derailed, Norfolk Southern said Monday.

The township’s police chief, Thomas Barndt, said containment booms were deployed after diesel fuel spilled into the river. Norfolk Southern called it a small diesel fuel leak “common when locomotives are involved” that would be “vacuumed out.” Norfolk Southern also said plastic pellets that spilled from one car mostly fell onto the ground.

The safety board sent a team including “experts in train operations, signals and train control, mechanical systems, and human performance” and said late Sunday afternoon in a statement that investigators had examined the derailed cars and other train equipment.

Investigators had also been reviewing data from the locomotive event recorders and downloading data from the wayside signals, the safety board said. Downloads from the inward- and outward-facing image recorders on all three trains will be sent back to the organization’s Washington headquarters for further analysis, the safety board said.

Federal transportation authorities said they had released the site “to allow Norfolk Southern to move the rail cars and locomotives and for track repair work to begin.” Norfolk Southern said Monday that “site cleanup and track work resumed Sunday afternoon” after the safety board released the site to the company.

Officials said investigators would be at the scene for several more days, interviewing crew members and gathering other information. A preliminary report detailing factual information gathered will be issued in three weeks and a final report detailing a probable cause and any contributing factors is expected in 12 to 24 months, the safety board said.

Norfolk Southern said Monday that the company “quickly responded” to the derailment that “resulted in no harm to the community and no hazardous material concerns from the railcars.”

“We take this incident seriously and work hard to avoid all accidents,” the company said in a statement, vowing to work closely with federal authorities “to understand how it happened and prevent others like it.”