Early reports suggest there were up to three explosions on residential streets in the business district of Saint Gilles.

The Mirror is reporting two explosions were heard on streets in the business district of Saint Gilles, but they may have been caused by a number of cars that appear to be on fire.

There are no confirmed reports of what caused the explosions or whether they are part of a terrorist attack.

The blasts took place around midnight, Belgium time, near a popular cafe in the Belgian capital.

Belgium has been on high alert for months after terrorists linked to the November Paris attacks were traced back to Brussels.

In March, explosions ripped through Belgium's international airport and a metro station in the city centre, killing 32.

The Department of Foreign Affairs and Trade warns Australian travellers to exercise a "high degree of caution" in Belgium and France due to the high threat of terrorist attack, its strongest warning in western Europe.

Photos and videos posted to social media show several vehicles ablaze, in a line down the street.

It's believed some of the fires have been brought under control by firefighters.

Several cars blazed but firemen quickly put out the fire; now everything in the street is relatively calm— Antonella Zarra (@anti_zeta) July 13, 2016

And now the aftermath. Bravo, merci les #pompiers de Bruxelles! pic.twitter.com/P6dfKzMDJP— Atli Stannard (@atlistannard) July 13, 2016

Fire in #SaintGilles #Bruxelles: a line of cars burning. Firemen seem to be containing it. pic.twitter.com/KSU35xjgJ2— Atli Stannard (@atlistannard) July 13, 2016