At Kasumigaseki, one of the hardest hit subway stations, staff and relatives of some of those who died in the biggest attack on post-WWII Japan fell silent at 8:00 am to remember those who were lost and those still affected.
"Twenty years have passed but I think the victims are still suffering," said Fumiko Suzuki, who was there to pay tribute to a friend made ill by the invisible clouds of sarin that spread through rush-hour trains.
Prime Minister Shinzo Abe also visited the station in the afternoon to place flowers in memory.
"I offered my condolences to the victims as we marked the 20th anniversary of the attack," he said.
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"The incident isn't over yet because many are still suffering from the after-effects of the sarin."
Thirteen members of the Aum Supreme Truth cult remain on death row for their part in the March 20, 1995 terror and for other murders and kidnappings the group carried out.
Cult leader Shoko Asahara, a blind mystic who espoused a blend of Hinduism and Buddhism, was convicted of ordering five teams of followers to dump packets of sarin on trains, puncturing them with the sharpened tip of an umbrella.
Some died almost instantly, while others suffered gradually worsening symptoms.
More than 6,000 people were treated in hospital after having inhaled sarin -- an agent developed in Nazi Germany and used by Saddam Hussein against the Kurds in Iraq.
Kasumigaseki station master Mitsuaki Ota led tributes to Tokyo Metro worker Kazumasa Takahashi who unknowingly picked up a punctured packet of the nerve gas from the floor of one of the trains.
He and another colleague died.
Takahashi's widow, Shizue, told reporters that the 20th anniversary of the attack should serve as a wake-up call over the risk of terrorism.
"It's possible we'll face the danger of terror attacks. I want (Japanese people) to be more aware," she said after laying a flower on a makeshift altar.