Sydney: The hashtag #IllRideWithYou has been trending on Twitter in Sydney and other major cities as Australians reached out to support Muslim commuters amid the Sydney hostage crisis.

Australian public transport users are offering to act as buddies for anyone who might be nervous to appear in public wearing religious attire.

This follows the hostage crisis in Sydney where an armed gunman took several people hostage at the Lindt Chocolat Cafe at the height of the morning rush-hour. Five of the hostages, including two women, made it to safety.

A black flag with Arabic writing in white was held against the window of the cafe, fuelling speculation that it could be the work of an Islamic extremist.

According to reports, the flag appears to be a Shahada flag, which bears an inscription which means: "There is no god but God, and Mohamed is the messenger of God".

As news of the crisis spread, Sydneysider Rachael Jacobs wrote on Facebook: "...and the (presumably) Muslim woman sitting next to me on the train silently removes her hijab".

She added: "I ran after her at the train station. 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".

Tens of thousands of Twitter users already offered their support.

According to reports, an Australian woman started the #Illridewithyou hashtag to show solidarity with Muslims who might feel threatened on public transport.

@sirtessa tweeted:

She followed it with:

Within hours, Australians around the country repeated the hashtag, making #Illridewithyou one of the top trends on the social media site.

"I make a commitment, right now, to always say something when I see any kind of abuse on public transport. #Illridewithyou," one user tweeted.

Another user in South Australia wrote: "If you wear religious attire, & need to get from #Adelaide's west suburbs to the city on Tues but don't want to travel alone #Illridewithyou."

Another tweeted: "I'm in. If u wear religious garments & feel unsafe on public transport, I'll sit with u. Redfern-KX, peak hrs."

Polly Maeve wrote: "I only ride a short distance to and from the city on the Belgrave/Lilydale/Alamain lines, but #Illridewithyou. #racismstopswithme".

Sydney-based lawyer and prominent Muslim woman Mariam Veiszadeh told the Press Association that the movement was "heartwarming".

Mifrah Mahroof of Australia posted: "The #Illridewithyou hashtag makes me so proud to be Australian. Thanks for the support everyone."

Arif wrote: "This is my Australia. Being a Muslim, this hashtag is the best thing that happened today. I Love you Australia."