A fire that broke out at a house in Rotterdam early on Tuesday morning may have been caused by an explosive device put there deliberately, police have said on social media.

The fire broke out at 7 am following an explosion at a house on the Allard Pierson street in the Delfshaven area of the city.

According to police, a suspect “dressed in black” was seen running away. Witnesses said they heard several explosions. “I heard two quick bangs around 5.30 am. I also heard shouts,” one neighbour told the Telegraaf.

Another neighbour confirmed the fire had been reported early and that police and the fire services arrived quickly.

The fierceness of the fire meant some 40 people had to be evacuated to a nearby sports hall. Three people, who were reportedly saved by firemen using a hydraulic platform, were checked for the effects of smoke inhalation and other injuries by ambulance staff. Two of them had to be taken to hospital.

The fire brigade were still in the process of putting out the fire later on Tuesday morning and it is unclear when neighbours will be allowed back in their homes.

Mayor Ahmed Aboutaleb did not comment except to say he wants to wait for the results of the investigation.

There have been at least 250 firebombings in the Netherlands this year, mostly related to conflicts between drug gangs, although police think some are down to copycat behaviour or conflicts between neigbours and (business) partners. Most took place in Rotterdam and Amsterdam.