Brussels oldest mosque has been evacuated and decontamination units called to the scene after envelopes reportedly containing a "suspicious powder" were found inside.

The city’s fire brigade spokesperson Meys Stone told local newspaper Le Libre several envelopes containing “white powder” had been discovered inside the building, which is nearby to the European Parliament, but that the contents of the envelopes had not yet been determined.

Two rooms of the building – one of Brussels’ largest mosques and located inside the Molenbeek district – have been seal off as investigators work, using devices to detect anthrax or other harmful chemical substances. Initial scans revealed the substances were not radioactive, according to an AFP correspondent outside the mosque.

Pictures on social media showed a significant number of emergency service personnel outside.

Seven people, originally reported as 11, appear to have been transferred to hospital from the mosque. The individuals are believed to have been taken to the hospital as part of a decontamination procedure.

There have been conflicting reports as to whether the items discovered are packages or envelopes.