TOKYO (Reuters) - A woman invaded a sumo ring -- a sacred arena from which females are banned -- in Tokyo during a major tournament, domestic media said on Thursday, then was pulled down by a referee and one of the sport's huge wrestlers.

The middle-aged woman dashed from the side of the Kokugikan sumo stadium on Wednesday and shoved away a female security guard before rolling onto the ring just as a bout was set to begin, the Yomiuri newspaper said.

The Japan Sumo Association insisted that though the woman did enter the raised platform around the batting ring, she did not set foot on the ring, or dohyo, itself.

"It's bad for the heart," said Takamisakari, a popular wrestler who helped catch the woman, told the Sports Nippon daily. "What was the person trying to do while we were wrestling seriously?"

It was not clear why she had attempted to reach the ring during one of the sport's heavily televised six big tournaments, but she was carrying a bundle of flyers saying "help, bad spirits," Nikkan Sports daily reported.

Such an intrusion would be a severe faux pas for the ancient sport, which is so serious about keeping females out that a female governor of Osaka had to delegate prize-giving duties to a male subordinate at a 2001 tournament.

Japan's giant wrestlers battle it out in a ring with a diameter of 4.6 meters (15 feet) set in the centre of a sand stage raised around 50 centimeters (19 inches) from the ground.

Tradition forbids women from entering the ring on the grounds that it is sacred and their presence, considered unclean, would pollute it.

"It's just the way it's been from the past," an official from the sumo association said.

Women were also banned in the past from climbing mountains or entering mines in Japan.