Seven members of a Japanese cult responsible for a deadly nerve agent attack on Tokyo's underground in 1995 have been executed.

The group’s leader Shoko Asahara was among those hanged on Friday – two decades after 13 people were murdered and more than 6,000 others injured in what remains Japan’s deadliest terror attack.

The hangings are the largest simultaneous execution in Japan since 1911, when 11 people were hanged for plotting to assassinate the emperor.

Chemical attack

In total, 12 followers had been on death row with Asahara after members of the cult punctured plastic bags to release sarin nerve gas inside train carriages in five co-ordinated attacks.

They targeted underground lines, including those passing through Kasumigaseki and Nagatacho, home to the Japanese government.

Atsushi Sakahara, who was injured in the attack, welcomed the executions.

"When I heard the news, I reacted calmly... but I did feel the world had become slightly brighter," he said.

"I've been in pain for years. It will be impossible to ever forget the incident, but the execution brings a kind of closure."

Aum Shinrikyo

Founded in 1984, the Aum Shinrikyo cult attracted many young people, even graduates of top universities, whom Asahara hand-picked as close aides.

It amassed an arsenal of chemical, biological and conventional weapons to carry out Asahara's escalating criminal orders in anticipation of an apocalyptic showdown with the government.

The cult claimed to have 10,000 members in Japan and 30,000 in Russia but has disbanded.

However nearly 2,000 people still follow its rituals in three splinter groups, closely monitored by authorities.