Russian President Vladimir Putin yesterday said an explosion that tore through a Saint Petersburg supermarket, wounding 13 people, was an act of terror, as footage of the suspected bomber spread on the internet.

Speaking at a meeting with military officers in the Kremlin, Putin ordered the nation's security services to "act decisively" and "liquidate bandits on the spot" if armed militants put up resistance.

His spokesman Dmitry Peskov told reporters later that the Russian leader was referring to all those "who harbour plans to carry out acts of terror in our country."

On Wednesday evening, a homemade bomb placed in a locker at the supermarket in northwestern Saint Petersburg, Russia's second city and Putin's hometown, exploded.

"As you know, an act of terror took place in Saint Petersburg yesterday," Putin said at a ceremony to award officers who took part in the Syria campaign.

Those wounded in the attack included a 35-year-old pregnant woman.

Putin's 2015 decision to intervene in Syria militarily on the side of Bashar al-Assad has made Russia a priority target for the Islamic State group.

Anna Mityanina, vice governor of Saint Petersburg, said on Twitter that six people remain in hospital care.

The bomb came after the FSB security service said earlier this month it had prevented a terror attack on a key Orthodox cathedral in Saint Petersburg with the help of America's CIA, which led Putin to thank US President Donald Trump.

An interior view of the supermarket is seen after the explosion that left 10 people injured. Photo: Reuters

The explosion occurred at around 1845 local time (1545 GMT) as people geared up to celebrate the New Year -- the country's biggest holiday -- followed by Russian Orthodox Christmas, which falls on January 7.