By Johan Ahlander and Helena Soderpalm

GOTHENBURG, Sweden (Reuters) -Four people were seriously hurt in an explosion and fire in a central residential area of the Swedish city of Gothenburg early on Tuesday.

Uncertain as to the cause of the fire and explosion was reported.

Fire fighters had to pull people from the smoke-filled residential block and take them to hospital.

A spokesperson for Sahlgrenska University Hospital said that three women and one male were taken to hospital with serious injuries.

Swedish public broadcaster SR stated that 25 people were transported to hospitals in and around Stockholm’s second city.

Although police confirmed that an investigation had been opened, they could not provide further information.

The emergency services stated that they are working to evacuate the people from the area and set fires. While they confirmed that there was no gas leak, they did not speculate as to the exact cause.

Anja Almen who lives in this building said that she heard an explosion from the street around 5:00 a.m. — 15 minutes after the explosion.

“I was shocked when I saw the explosion from my balcony. She said that smoke was everywhere from each stairwell, and she also heard from another nearby church. Tenants were then evacuated. People were being evacuated from their homes by fire trucks using ladders.

An emergency spokesperson stated that several hundred people had been evacuated around the area of the explosions and fires.

This Nordic country is currently dealing with a growing gang crime problem. Rival groups have been using fire arms and explosives to settle scores.