Russia attack: St Petersburg police find and deactivate second metro bomb

Device reportedly left in a briefcase

Emergency services direct pedestrians outside Sennaya Ploshchad metro station after an explosion that killed nine people (Reuters)

Russian security agencies have found and defused a second explosive device on the St Petersburg metro after an explosion killed at least nine people.

The device was left in a briefcase, the Interfax news agency reports.

Andrei Przhezdomsky, a spokesman for Russia's top anti-terror agency, said the improvised explosive was found at the Ploshchad Vosstaniya station.

An unidentified explosive device went off at 2:20pm on a train leaving the Technology Institute station and heading to the Sennaya Ploshchad station, Russia's National Anti-Terrorist Committee said.

The blast came as Russian President Vladimir Putin was visiting the city, his hometown. He said investigators are looking into whether the explosion was a terror attack.

News agency Interfax cited a source saying the blast was caused by a bomb filled with shrapnel.

Ambulances and fire engines descended on the concrete-and-glass Sennaya Ploshchad metro station near the centre of the former Russian imperial capital. A helicopter hovered overhead as crowds gathered.

The St. Petersburg subway immediately shut down all of its stations and the national anti-terrorism body said security measures would be tightened all key transport facilities across Russia.