LIGONIER, Ind. (AP) — A freight train hauling hazardous materials derailed in rural northeastern Indiana on Tuesday, causing a tanker to burst into flames that belched yellow smoke and prompting the evacuation of a handful of nearby homes.

Twenty-two cars came off the rails around 5:30 a.m. near the Noble County town of Ligonier, about 40 miles northwest of Fort Wayne, Noble County Sheriff Doug Harp said. He did not know what caused the derailment.

No injuries were reported.

A tanker containing liquid sulfur caught fire in the derailment and firefighters decided to let it burn because dousing it with water could wash the chemical into the nearby Little Elkhart River, Harp said. The fire was still ablaze after more than five hours and it was not immediately clear how long that would continue.

A second tanker carrying the gasoline additive toluene was also derailed. Forty-three of the train's 59 freight cars were loaded, according to Norfolk Southern spokesman Dave Pidgeon. Crews used heavy trucks to lift the derailed cars back onto the track.

Firefighters in breathing apparatus were assessing the scene, said Amy Hartsock, a spokeswoman with the Indiana Department of Environmental Management.

Harp said he didn't believe chemicals were reaching the river because they were flowing into stagnant water. He said three cars in addition to the sulfur tanker were leaking chemicals, but officials did not believe they were toxic. Hartsock said the area around the track is a wetland that feeds into the Little Elkhart River, but so far they've seen no sign of impact on aquatic life or waterfowl. She said foam on the river appeared to be natural and not connected to the derailment.

Authorities evacuated residents within a half-mile area as a precaution, Hartsock said. Harp told WANE-TV that about a half dozen homes were evacuated. Harp said crews were regularly checking the air quality in the area.

"The (public safety) risk is relatively low," Harp said.

Inah Schrock, who lives in a farmhouse along the tracks just southeast of the crash site, said she didn't hear the derailment but woke up with police and firefighters in front of her house. She said she wasn't worried because police told her she should be safe.

"They told me we should be OK with the wind direction," she said.

Toluene can affect the nervous system, according to the Agency for Toxic Substances and Disease Registry website. Inhaling high levels in a short time can cause light-headedness, dizziness, unconsciousness and even death. Exposure to high levels of sulfur dioxide can damage the respiratory system and be life-threatening, the website said.

More than 300 Amtrak passengers traveling to Chicago were briefly stranded in Ohio as the derailment closed the tracks along the way.

Amtrak spokesman Marc Magliari said two trains waited for three hours in Toledo. The Lake Shore Limited from New York and Boston has since been rerouted through Michigan and passengers on the Capitol Limited from Washington were transferred to buses.

Associated Press writer Charlie Wilson contributed to this report from Indianapolis.