Several people were injured and others trapped beneath debris after an explosion in the Belgian city of Antwerp on Tuesday.

Three houses were severely hit by the explosion in the southern suburb of Wilrijk.

The fire service said it still wasn't certain of the blast's cause, but Antwerp's mayor, Bart de Wever, tweeted that a "terrible gas explosion" had taken place.

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Three people have been rescued from the rubble and transferred to medical services. One of those rescued sustained serious injuries.

The city's fire department is working to free a third person, the fire brigade tweeted. The police force sent dogs to search for those who may still be trapped, they reported on Twitter.

Photos and police video of the scene showed a row of houses with a gaping hole. Local media quoted a local resident who said that when the explosion took place, construction had been taking place in one of the buildings.

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Police urged the public on Twitter to "avoid the area" to enable the police to "do their jobs." The local fire brigade said the Red Cross Flanders was on the scene to provide support for those affected.

Antwerp is a port city of roughly 500,000 people in the north of Belgium on the border with the Netherlands.

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mmc/msh (dpa, Reuters)