Belgian prime minister Charles Michel has asked everybody in Belgium to stay where they are and not travel. Stricter checks have been introduced on the Belgian-French border. Cars crossing to the Netherlands are also being checked. 225 extra soldiers have been deployed to ensure security. Mr Michel is expected to cancel his trip to China that was to start on Thursday.
Meanwhile the Belgian authorities have declared three days of national mourning.
Following the attacks public transport is at a standstill in the Belgian and Flemish capital. Rail stations Central, Zuid, North and Schaarbeek have been closed. Public transport in the capital has been suspended. International rail services are affected too. The Thalys and Eurostar services have been suspended for the day. Antwerp Central Station was evacuated but has now been reopened.
Trains heading for Brussels are being stopped in stations outside the capital. In Brussels the North South rail link is closed and a number of trains will be diverted around Brussels centre.
Services of De Lijn in Flanders are operating normally.
Belgian mobility minister Galant has announced that Brussels rail stations will reopen at 4PM.
One of the other measures taken in Brussels has been to keep all school children locked in their schools. There are no specific indications that schools may be targeted. Schools should open normally in Brussels on Wednesday.
Belgian deputy premier Alexander De Croo has asked people not to use the telephone as the networks cannot cope with the traffic and to allow the emergency services to do their work. Mr De Croo asks people to use social media instead.
Several stores and shops have decided to close for the day.
Bart De Wever, the leader of Belgium's largest party, the Flemish nationalist N-VA, has said that today is the darkest day in Belgian history since the end of the Second World War.
The Belgian authorities are operating the 1771 emergency number for people seeking information about casualties.
A massive police and military presence has been deployed in Brussels that for the rest looks pretty much like a deserted city. Police helicopters are overflying the capital where house searches are underway in a bid to locate the surviving perpetrators. Police have asked the media not to give details of this operation.
A controlled explosion has occurred near the Wetstraat after police found sacks of clothes outside the royal palace. The controlled explosion was staged by the bomb disposal squad as a precaution.
During a news conference Brussels police said that they cannot yet confirm a precise number of casualties. There are fatalities in the Maalbeek metro explosion, many injured too.
Police, fire-fighters, the Red Cross and other emergency services are at Brussels Airport and the Wetstraat where the Maalbeek metro station is located.
Police are asking everybody to stay indoors. There is no public transport in Brussels at the minute, though rail services should start to resume around 4PM to allow commuters to get home.
European civil servants evacuated
Staff at the Berlaymont Building, the headquarters of the European Commission, located not far from the scene of the Maalbeek metro attack, are being evacuated from the building.
Staff are being led away from the Berlaymont under police escort.