The attack saw a man take customers and staff hostage at the cafe and they could be seen through the cafe's windows with their hands held in the air, while heavily armed police surrounded the building.

A number of hostages were being forced to hold an Islamic flag that has been co-opted by jihadist groups flag against the window shortly after the siege began at 9.45am.

Following this the #illridewithyou hashtag amassed more than 22,000 tweets on Monday evening, as Australians took a stand against anti-Muslim sentiment in the wake of the Martin Place siege.

A young Sydney woman, Rachael Jacobs, appears to have inspired the campaign after posting a moving Facebook status about her encounter with a Muslim woman earlier in the day.

"...and the (presumably) Muslim woman sitting next to me on the train silently removes her hijab," Ms Jacobs wrote.

"I ran after her at the trainstation. I said 'put it back on. I'll walk with u'. She started to cry and hugged me for about a minute - then walked off alone."

The inspiring status quickly circulated on social media, before being picked up by another young Sydney woman on Twitter, known only by her handle @sirtessa, who made this offer to members of the muslim community.

The hashtag was soon trending and since then there has been thousands more similar offers and posts on social media with the #illridewithyou hashtag.

Have a look at some of the posts below.