Two explosions have hit the Brussels Zaventem airport, killing up to 13 people and injuring dozens, hospital sources told local media.

Shortly after the airport blasts on Tuesday morning, an explosion also struck at a metro station in the center of the Belgian capital, close to European Union institutions.

There were unconfirmed reports of attacks at other metro stations.

Footage from the airport showed people running from the terminal building as plumes of smoke rose to the sky.

The powerful blasts at the country's main international airport caused parts of the ceiling to fall down and windows were shattered.

All metro lines were shut down after the blasts. Some witnesses at the Maelbeek said people with blood on their faces were seen at the scene.

The interior ministry raised the country's terror alert to the highest level after the blasts and Brussels crisis center told people, "Stay where you are".

State broadcaster VRT reported that a suicide bomber had detonated explosives at the airport.

Reuters news agency reported that shots were fired before the explosions went off.

Local media reported that the blasts happened near the American Airlines as hundreds of people were checking in.

Al Jazeera's Neave Barker, reporting from the airport, said there were dozens of ambulances at the scene and police were clearing the area of stranded passengers, some in shock.

The country had been on high alert since the arrest in Brussels last week of Salah Abdeslam , a key suspect in last year's Paris attacks that left 130 people dead.

PHOTO CAPTION

Black smoke is seen rising from the Brussels airport following explosions, in this still image made available March 22, 2016.

Al-Jazeera