Fifteen people were taken ill due to noxious fumes in the kitchens of the EU's new Europa building in Brussels, where leaders of the bloc are due to hold a summit next week, emergency services said.
Ambulances were seen outside the 321-million-euro headquarters of the European Council, dubbed the "Space Egg" because of its futuristic oval interior shape, and five people were taken to hospital, they said.
"There was a bad mix of chemical products on the kitchen level. That caused fumes which made 15 people sick," Pierre Meys, a spokesman for Brussels emergency services, told AFP.
He said the symptoms included "sore eyes and vomiting".
The European Council confirmed the incident but said next week's summit of 28 European Union leaders would take place there as planned.
"A technical issue affecting the ventilation in the kitchens of the Europa building, producing noxious fumes in the kitchens, has led to a number of kitchen staff falling ill," the council said in statement.
"The Belgian firemen and medical services were brought in today to investigate the situation and evacuate kitchen staff who felt ill."
Staff were evacuated to the neighbouring Justus Lipsius building "applying the principle of safety first" it added.
"This incident will not prevent next week's meeting of the European Council from going ahead," it said.
The ambulances were deployed as part of an "emergency medical plan" created by local authorities for any incident involving more than 10 people, he added.
The Europa building opened in January after a series of delays.
© 2017 AFP