Commuters flee through smoke-filled tunnel after Brussels metro blast

Train commuters in Brussels have been forced to traipse through a smoke-filled tunnel to safety after a bomb was detonated at a metro station in the city's centre.

At least 10 people have reportedly been killed in the overnight blast at Maelbeek Metro Station, Belgian broadcaster VTM reports.

The explosion is one of three blasts confirmed to have rocked Brussels, with the first two tearing through Zaventem airport earlier in the day.

Witnesses said they were evacuated after the station filled with smoke, while passengers aboard the train were told to get off and walk the tracks to the next station.

In amateur footage taken inside the tunnel, passengers walk gingerly down the tunnel, the dull steel of the tracks being picked up by the glare of the tunnel lights.

A man in a long jacket and backpack can be seen carrying a bouquet of fresh flowers.

"The metro was leaving Maelbeek subway station when there was a really loud explosion," witness Alexandre Brans told AP.

"It was panic everywhere. There were a lot of people in the metro." Metro company STID has announced all metro stations are now closed, The Independent reports.