The church had equipment to detect fires originating on the inside. The fire brigade was informed by a taxi driver passing by: the fire alarms went into action two minutes later.
The fire caused extensive damage to the 15th century building. The roof was destroyed completely, and collapsed onto the interior ceiling. However, the main structure and arched ceiling of the cathedral remained intact, and the interior was largely spared. There was some smoke damage, but no water damage.
Firefighters allowed the roof to burn in a controlled fashion, as it was feared that large amounts of water could cause the ceiling to collapse destroying the valuable interior. This strategy apparently proved successful.
The cathedral is located in the historical Old Town of Porvoo, where most buildings are made of wood. There were fears of a major disaster if the flames had spread.
There were no injuries in the blaze.