The area is currently full of heavily armed police, who have surrounded the building.
A NSW Police spokeswoman said that officers were called to the shop at around 9.45am this morning, and urged people to avoid the area as much as possible.
Reports suggest that there could be two gunmen inside the café – although this is yet to be confirmed by police.
In light of the situation, employers are encouraged to consider sending employees home if they are based in the CBD.
Additionally, HR managers and managers should advise staff to modify their meeting plans, avoiding Martin Place or venturing into the CBD.
The police have cleared the area surrounding the café. Evacuations of surrounding buildings have also been underway.
Employers are also advised to ensure that their employees know to expect delays if travelling in Sydney today. Efforts should also be made to get in touch with any employees travelling around Sydney to meet with clients or for other purposes.
According to Fairfax Media, the federal government has convened a meeting of the National Security Committee this morning.
Hostages are being forced to hold up an Islamic flag against the window of a café in Martin Place, Sydney.