Channel 7 evacuates newsroom

The Seven Network has been forced to evacuate its Sydney newsroom in Martin Place due to a man holding people hostage at a nearby café.

The media company's newsroom and location for its Sunrise and The Morning Show programs is directly opposite the Lindt café where the siege is currently taking place.

It is understood as many as 20 hostages are being held in the café by a man armed with a shotgun with potential links to terrorist organisations.

Hostages inside the cafe have been forced to hold what appears to be an Islamic flag, identified as a shahada flag, in the cafe's window reading "no god worthy of worship except Allah and Muhammad is his messenger".

It is not yet known whether any of the hostages are Seven Network employees.

Businesses that share the same Sydney CBD office building as the café are yet to be evacuated as they await police instruction.

It is understood that staff of a number of businesses in 53 Martin Place are remaining in their offices and have been in contact with police through their building management.