Sheriff Wayne Gallant said the pickup driver, who was not seriously injured, may have been blinded by the setting sun.
Gallant said the accident happened just before 8 p.m. Monday on Rt. 117 in Buckfield. He said the girls were thrown from the buggy. A man driving the buggy suffered a broken leg.
He said the girls, whose names have not been released, are believed to be sisters who were visiting from the Lewiston-Auburn area. The older girl was flown to Maine Medical Center in Portland.
Gallant said the accident is still under investigation.