BUFFALO, New York (Reuters) - A charter bus of Polish tourists overturned in upstate New York, injuring as many as 19 passengers, and police said on Thursday they were investigating how fast it was traveling on a rain-slicked highway,

The bus carrying a Polish tour group between Niagara Falls, New York, and Trenton, New Jersey, veered off a section of Interstate 81 north of Binghamton, New York, amid a heavy downpour at 7 p.m. on Wednesday, said State Police Captain Eric Janis.

"It was raining very hard at the time of the accident. We're looking at the weather. We want to see if the speed was appropriate for the weather conditions," he said, stressing that no official cause has yet been determined.

Between 14 and 19 passengers were taken to area hospitals for treatment of minor injuries and all were released, he said.

"One person was actually pinned under the bus. They were able to get her out and she suffered a minor head laceration," he said.

Janis acknowledged a recent rash of tour bus accidents throughout the state, and said state Department of Transportation officials were working with investigators to complete a thorough safety inspection of the bus, operated by a company called Amerpol Tours based in Morrisville, Pennsylvania.

(Reporting by Neale Gulley; Editing by Barbara Goldberg and Jerry Norton)