Officials in Sweden have vowed to determine why a man killed 10 people, and apparently himself, in an unprecedented attack that's shaken their "society to its core."

Five people have been shot at a school in Sweden as authorities warned the danger was not over while armed officers rushed to the scene. Armed police descended on the Risbergska School, an adult educational institute in the city of Örebro some 200 km (125 miles) west of Stockholm on Tuesday.

All Swedish schools and pre-schools will have to make plans to keep unauthorised people off their premises, the government said on Wednesday, as the country tries to come to terms with the worst school shooting in its history last week.

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 center where the attacker appeared to have used several of his own licensed rifles.

The shooter targeted a center that serves migrants seeking to integrate into a country that had already reversed its liberal migration policies.

Government offices, schools and workplaces fell silent in Sweden at midday on Tuesday in remembrance of the victims of a mass shooting at an adult education centre last week when a gunman killed 10 people before turning his weapon on himself.

A minute's silence was observed across Sweden on Tuesday to honour the victims of a deadly shooting at an adult education centre in the city of Örebro. The minute's silence was held in Örebro and several other Swedish cities at 12 pm (1100 GMT).