TOKYO (AP) - A disc-shaped piece of ice of unknown origin plunged from the sky onto a golf course near Tokyo on Wednesday, narrowly missing players on the fairway but causing no injuries, police said. Authorities were investigating the bizarre incident, said Saitama prefectural police spokesman Masahiko Kuwashima. Four players at the Heisei Club golf course in Saitama, just outside Tokyo, heard a loud thud and found a disc-shaped hunk of ice - about 50 centimetres in diameter and 15 cm thick - broken into several pieces, Kuwashima said. He said investigators have asked the Transport Ministry to check the possibility that ice stuck on an airplane may have fallen. There have been several reports of ice falling in Chiba prefecture near Tokyo's Narita International Airport, Kuwashima said. But there is no airport in Saitama, and the golf course involved Wednesday is not known to be beneath a flight route, he said. "It's puzzling," Kuwashima said, adding that the ice, which weighs two kilograms, is being kept in a police department freezer.