By Brenna Hughes Neghaiwi

ZURICH (Reuters) - Six people were injured in an attack aboard a Swiss train on Saturday by a man armed with a knife and flammable fluid, St Gallen cantonal police said.

Three adults, two teenagers and a child aged six were hurt, according to a police statement. Five were stabbed or burned. A sixth suffered smoke inhalation as he came to the aid of the others. The assailant, a Swiss citizen, was also injured.

"According to current information, a 27-year-old Swiss man poured out a flammable liquid. He was also armed with at least one knife. The liquid caught fire," the statement said.

Authorities did not yet know the motive for the attacks but a crime of passion was one possibility, Bruno Metzger of the St Gallen cantonal police said in an interview with

"A terrorism background still seems very, very far-fetched," Metzger said.

The assailant was in police custody, he said, but none of those injured - including the assailant - was responsive, so they could not be questioned.

The police said a criminal inquiry was under way.

Both a woman and the attacker were in critical condition, according to Swiss broadcaster SRF, citing the St Gallen police. The cantonal police did not respond to a request for further information by email and could not be reached by phone.

The attack occurred at 2:20 p.m. (08:20 a.m. EDT) as the train neared the Salez station on a trip between Buchs and Sennwald in St. Gallen, a canton in the northeast of the Alpine republic, the police statement said.

It was the first attack of its kind in Switzerland in recent memory. In December 2015, a 33-year-old Swiss man broke into his neighbors' house in Rupperswil and killed four people before setting the house on fire, an incident that shocked the country.

(Reporting by Brenna Hughes Neghaiwi, additional reporting by Michael Shields,; editing by Larry King)