The death toll from a lorry crash in the Netherlands rose to seven on Wednesday as local authorities confirmed that an unborn child was also killed when the vehicle drove off a dike and ploughed into a neighbourhood barbecue over the weekend.

Local mayor Charlie Aptroot said in a statement: “The loss is immeasurable and the grief immense.

“So far, we have talked of six deaths, including one heavily pregnant woman. In consultation with the relatives, we have decided from now on to talk about seven deaths, including one unborn child.”

Police initially said that three men and three women were killed, ranging in age from 28 to 75, in the crash. A further seven people were hospitalised, one of them critically.

The driver of the truck, a 46-year-old Spanish man, was taken into custody by police on suspicion of causing the crash that happened on Saturday evening in the village of Nieuw-Beijerland, just south of the port city of Rotterdam.

His identity has not been released, in line with Dutch privacy laws.

The lorry careered down the side of a dike and into the middle of a barbecue attended by dozens of people from the close-knit local community. Police are investigating the exact cause of the crash.

Mr Aptroot said the community was in deep mourning and he opened a condolence book at two local town halls and online.

“Let’s hold each other and be there for each other,” he said.