Mr De Croo and his interior minister, Annelies Verlinden, were reported to have arrived at the centre following the attack.
Mr De Croo said: “My most sincere condolences to the loved ones of the victims of the cowardly attack in Brussels.
“I am currently with the ministers of justice and the interior at the national crisis centre.
“We are monitoring the situation and asking Brussels residents to be vigilant.”
Officials were meeting in the early hours of Tuesday to decide on whether schools and offices in the Belgian capital will be able to open in the morning if the alleged terrorist is still on the loose.
The National Crisis Centre earlier upgraded Brussels’ warning level to four, the highest level, recommending against any unnecessary travel around the capital. Ocam, the body that coordinates threat levels in Belgium, raised the rest of the country to level three.
