This image from the Brussels Airport surveillance cameras made available by Belgian Police, shows what officials believe may be suspects in the Brussels airport attack on March 22, 2016. The Belgian state prosecutor said in a press conference on Tuesday, that a photograph of three male suspects was taken at Zaventem. "Two of them seem to have committed suicide attacks. The third, wearing a light-colored jacket and a hat, is actively being sought," the prosecutor said. [Photo: CRI Online]

Belgian media are reporting that a key suspect in the terror attack in Brussels on Tuesday morning has been arrested.

Najim Laachraoui is believed to be the man on the right in a CCTV image taken before the suicide explosion at Zaventem airport.

Meantime, Chinese leaders have strongly condemned the terror attacks in Brussels while extending condolences to the victims and their families.

In his message to King Philippe of Belgium, President Xi Jinping expressed China's willingness to step up security and anti-terror cooperation with Belgium, stressing that the international community should work together to address the root causes of terrorism.

Meanwhile, Premier Li Keqiang sent condolences to his counterpart Charles Michel.

Li Keqiang also reiterated China's stance against terrorism while meeting with leaders from some Southeast Asian countries.

"We want to express condolences to the victims in the attack. Also we want to express sympathy to the families of the victims and the wounded. China, like all the others, is against all forms of terrorism. We are willing to make joint efforts with the international community to maintain world peace and regional stability."

The attack in Brussels led to prime minister Michel cancelling a scheduled trip to China.

Police are still hunting for two suspects, identified as brothers, and who are known to police.

The pair have been identified as Khalid and Brahim el-Bakraoui.

It is believed at least one of them was among the three suspects seen in a surveillance video at Zaventem airport.

Belgium is observing three days of national mourning for the 34 people killed and more than 200 others injured in the attacks.

The Islamic State group has claimed responsibility for the blasts at the airport and at a metro station, and has warned that more will follow.

The attacks sent shock-waves across Europe and around the world, with authorities racing to review security at airports and on public transport, and rekindled debate about European security cooperation and police methods.