Russian President Vladimir Putin has blamed a mass shooting at a college in Crimea on globalisation.

Key points: The 18-year-old gunman died from a self-inflicted gunshot after killing at least 20

The 18-year-old gunman died from a self-inflicted gunshot after killing at least 20 He "could not have prepared this attack on his own", according to Kremlin-appointed head of Crimea

He "could not have prepared this attack on his own", according to Kremlin-appointed head of Crimea Deputy head of FSB said the security services need greater control over the internet

He said the problem that began in the United States has spread around the world through online communities on the Internet.

An armed 18-year-old student in the Black Sea port city of Kerch killed 20 people, most of them fellow pupils, and wounded dozens at his college, law enforcement officials said.

The suspected attacker was found dead from a self-inflicted gunshot wound after an attack that also saw a bomb set off in the college canteen.

A second explosive device was found among the suspect's personal possessions.

Vladislav Roslyakov was initially described as the only person involved in the carnage at the school.

But Sergei Aksyonov, the Kremlin-appointed head of Crimea, told Russian news agencies it is still possible the student had help.

"The point is to find out who was coaching him for this crime," Mr Aksyonov said.

"He was acting on his own here, we know that. But this scoundrel could not have prepared this attack on his own, in my opinion, and according to my colleagues."

"By all appearances this is the result of globalisation, as strange as that may seem," Mr Putin said at a forum in the Black Sea city of Sochi.

Russian President Vladimir Putin believes the shooting was a result of globalisation. ( AP: Alexei Druzhinin )

"Everything started with well-known tragic events in schools in the United States. Young people with unstable minds create false heroes for themselves," he said.

"This means that we all, not just Russia, but we across the world are reacting badly to changing conditions in the world," Mr Putin said.

"We are not creating necessary, interesting and useful content for young people."

Grieving residents gathered in Kerch, laying flowers and lighting candles to mark a three-day official mourning period declared in the region.

Orthodox priests sang prayers in the street, leading a memorial service near the college.

"Where were the guards?" a tearful woman at a memorial asked.

"Where were the men who were there in large numbers? Why was it children who were shot dead at point blank?"

The attack at a college in Crimea has killed 20 people. ( AP Photo: Str )

Cyberspace

The death toll, including Roslyakov, has risen to 21, Russian agencies cited the Russian Health Ministry as saying.

The Russia-backed government in Crimea published a list of the victims, most of whom were teenagers.

Russia annexed Crimea from Ukraine in 2014, prompting international condemnation and Western sanctions, but since then there have been no major outbreaks of violence on the peninsula.

The first deputy head of Russia's Federal Security Service (FSB) said the security services needed to have greater control over the internet.

"For us professionals, it has long been evident that the cyberspace must be under the control of the relevant authorities," Sergei Smirnov said.

"Without this, it's impossible to guarantee the provision of information security and to combat modern terrorist threats in time."

AP/Reuters