Brussels airport
Black smoke is seen rising from Zaventem airport in Brussels following the explosions of 22 March 2016Peter van Rossum/Reuters

World leaders have responded with shock, concern and solidarity after several deadly explosions hit Brussels in a suspected terrorist attack on European soil. At least 13 people are reported to have been killed by two blasts that ripped through the departure hall of Zaventem airport in the Belgian capital. All flights have been cancelled and inbound planes diverted elsewhere.

Explosions were also heard later on the city's Metro system. The terror alert in the northern-European country has been raised to maximum.

Belgian Prime Minister Charles Michel wrote:

British Prime Minister David Cameron tweeted:

He was echoed by his Italian counterpart, Matteo Renzi, who wrote (translated): "with heart and mind to Brussels, Europe."

Ukrainian president, Petro Poroshenko, sent his condolences to the families of the victims.

British foreign secretary Philip Hammond described the attacks as an act of "senseless violence".

Russian Prime Minister Dimitry Medvedev said the blasts were "a barbaric crime against civilians".

Lithuania's president Dalia Grybauskaitė, described the blasts as a "terrible act of terrorism", while former labour leader Ed Miliband said he was "shocked and saddened" by the news.

French president Francois Hollande said: "I express my full solidarity to the Belgian people. It is the whole Europe that has been hit by the attacks in Brussels."

Former French PMs François Fillon and Alain Juppé sent messages of solidarity for their Belgian neighbours.

"Solidarity with Brussels. Radical terrorism is a cancer. Europe must stand togheter," tweeted Fillon (translated).

"Solidarity with the Belgian people after the explosions in Brussels and at Zaventem airport. Support to rescuers and injured," wrote Juppe (also translated).

The President of the European council Donald Tusk said the EU will help Belgian authorities as well as other European government to counter the terror threat. "I am appalled by the bombings this morning at Zaventem airport and the European district in Brussels which have cost several innocent lives and injured many others," he wrote in a statement. "I extend my sincerest sympathies to the relatives and friends of the victims. These attacks mark another low by the terrorists in the service of hatred and violence."