Panic erupted in Yokohama's main train station this morning when a mysterious gas spread through an underground passage, sickening at least 261 people.Aum Shinri Kyo, the Japanese cult suspectedin theMar. 20 nerve gas attack on Tokyo subways, immediately denied any involvement. Thousands of commuters poured out of the station, jamming sidewalks and streets, while sirens wailed and about 10 police helicopters circled overhead. Police, firefighters and chemical weapons experts, some wearing gas masks, were checking the station for the source of a foul chemical odor. (A college student told the Associated Press she saw firefighters clad removing 20 or 30 small cardboard boxes from the station.) Officials said sarin, the nerve gas used in the Tokyo attack, was not suspected because the victims' symptoms were different. People affected by the fumes today complained of stinging eyes, coughs and dizziness, but there were no reports of serious or life-threatening injuries. Curiously, on Mar. 5 -- two weeks before the Tokyo attack raised national alarm -- about a dozen passengers were taken to a hospital in Yokohama after they inhaled mysterious fumes in a train car. The source of the fumes was never found.