PARIS—A school undergoing construction work collapsed in the Belgian city of Antwerp, killing five workers and injuring nine others, according to local authorities. An investigation is underway into the cause of the accident. Firefighters and rescue dogs labored through the night after Friday’s accident to pull out the victims one by one, while the construction company cleared rubble and worked to secure the site, according to a running account on Twitter by the Antwerp fire service. As of Saturday, all the construction workers who had been at the site had been accounted for. Of those injured, three were in intensive care, five others were hospitalized, and one had been released, according to the fire service. Belgium’s King Philippe and Prime Minister Alexander de Croo visited the site Saturday. Belgian media reported that the workers included citizens of Portugal, Romania, and Ukraine.