European shares fell in early trading on Tuesday, with travel and leisure stocks leading the market lower after explosions hit the airport in Brussels, according to the Daily Mail.

The STOXX Europe 600 Travel and Leisure index fell 2.2 percent, the top decliner, with shares in easyJet, Ryanair, Accor, InterContinental Hotels and IHG down by 2.4-4.6 percent.

The pan-European FTSEurofirst 300 index was down 0.7 percent, while Belgium's benchmark share index was down 0.5 percent. 

Several explosions have struck Brussels airport and the metro system, causing at least 13 deaths, Belgian media say.

Two blasts tore through the departures area of Zaventem airport shortly after 08:00 local time (07:00 GMT).

An hour later, an explosion hit Maelbeek metro station, close to the EU institutions. The airport and whole transport system have been closed.

The attacks come four days after Salah Abdeslam, the main fugitive in the Paris attacks, was seized in Brussels.

The Belgian government says there have been casualties at the airport but has given no numbers. The cause of the explosions has not been confirmed.

Belgium has now raised its terror threat to its highest level. Prime Minister Charles Michel tweeted: "For the moment, we are asking people to stay where they are."