Russian officials are combing through the cafe where a pro-Putin blogger was killed in a suspected assassination.
Vladlen Tatarsky, whose real name is Maxim Fomin, died in St Petersburg on Sunday after being handed a statue of himself by a woman, which was believed to contain 200g of TNT explosives.
A video posted on Russian messaging app channels showed the cafe after the explosion. Tables and chairs were broken and stained by blood, and shards of glass littered the floor.
Approximately 100 people were at the Street Food Bar No 1 for a political event when the blast occurred, injuring at least 30 people, five of whom are in critical condition.
Eyewitness Alisa Smotrova described people running in panic, some hurt by shattered glass and covered in blood.
Russian media said investigators were looking at the statue as the possible source of the blast but have not ruled out the possibility that an explosive device was planted in the cafe before the event.
An investigation has been opened by Russia's state Investigative Committee, while analysts in the country have suggested that the attack was carried out by the Ukrainian secret service.
A purported witness to the attack said how a woman who identified herself as Nastya said that she had made a bust in Tatarsky's likeness, but guards asked her to leave it at the door out of concern that it could be a bomb.
Nastya and Tatarsky reportedly then joked and laughed before she went to the door, picked up the bust and presented it to Tatarsky.
He put the item on a table before an explosion ripped through the cafe.
Russian media outlets report that investigators are considering all options as to the source of the explosion, including the theory that a bomb was planted in the premises prior to the event.
No one has claimed responsibility for the attack but military bloggers and patriotic commentators immediately pointed a finger at Ukraine and compared the bombing to the killing last August of Darya Dugina.
Russian authorities blamed Ukraine's military intelligence for Dugina's death in a car bombing near Moscow, but Kyiv denied involvement.
Dugina's father, Alexander Dugin, a nationalist philosopher who is a staunch supporter of Putin's invasion of Ukraine, hailed Tatarksy as an "immortal" hero and a martyr for the Russian people.
"There must be no talks with the terrorists other than about their unconditional surrender," Dugin said. "'A victory parade must take place in Kyiv."
