Sweden's right-wing government said on Friday it would seek to tighten gun laws in the wake of the country's deadliest mass shooting at an adult education centre where the attacker appeared to have used several of his own licensed rifles.

The police responding to the attack encountered firing so intense that they struggled to tell how many gunmen were on the scene, an official said.

The government says it is seeking to strengthen vetting for gun licenses and restrict access to semi-automatic weapons.