(CNN) -- A social media campaign condemning Islamophobia under the hashtag #illridewithyou has taken off after an armed man who may have links to radical Islam took hostages in Sydney.
Anti-Muslim sentiment flared as chilling images from Australian media showed people, believed to be hostages, with their hands pressed against the glass of the Lindt Chocolate Cafe in Sydney's central business district. They were holding up a black flag with Arabic writing on it reading, "There is no God but God and Mohammed is the prophet of God." The gunman reportedly was demanding an ISIS flag.
There were fears that Australian Muslims could become the targets of racially motivated retaliatory attacks.
Instead Australian Twitter users offered to accompany Muslims wearing religious clothes on public transport as a gesture of solidarity under the hashtag #illridewithyou.
The campaign started with a tweet from @sirtessa, a TV content editor and writer from Sydney whose real name is Tessa Kum. "If you reg take #373 bus b/w Cogee/Martin Pl, wear religious attire, & don't feel safe alone: I'll ride with you. @ me for schedule," she wrote.
Kum told BuzzFeed News that "her heart broke" after reading a story tweeted by Rachael Jacobs as news of the hostage siege broke.
Jacobs had tweeted that "....and the (presumably) Muslim woman sitting next to me on the train silently removes her hijab ... 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."
Kum added: "It is hard to feel hope when you feel helpless. #illwalkwithyou is a small act, but might be important for someone one day ... For those of us watching; we live in this world. We aren't bystanders. We aren't helpless."
Kum received such a strong response to her initial tweet that she quickly suggested using the #illridewithyou hashtag, and tweets started coming in from all over Australia and beyond.
One Twitter user @Jamus_ wrote: "Any Muslim person getting the Geelong line (rail line in Melbourne) in the morning, #illridewithyou if you'd like me to. 6:47AM from southern cross."
Another one, Terri, said she would be wearing a scarf around her wrist so that any Muslims who wanted to travel with her would know who she was: "I'm a semi regular commuter on the #mandurah line. If you see me #illridewithyou. I'll be wearing this scarf."
The hashtag quickly began to trend and turned into a place for people to show their support and speak out against racism and Islamophobia.
Nikos de Serf from Melbourne tweeted: "We are all Australians & we will not turn away from our Muslim brother, sisters, fathers, mothers, loved ones & friend #illridewithyou all."
Phil Burgess, an Australian living in the United Arab Emirates, tweeted: "We live in Abu Dhabi but I am proud to say that #illridewithyou anytime!"
In a few hours, #illridewithyou has become the top trending hashtag globally and has been mentioned 150,000 times, including retweets, in the past 24 hours, according to social search and analysis site Topsy.
Muslims in Australia and across the world have shown their gratitude for the campaign.
One user, Angger Prawitasari, wrote: "Thanks for protecting my sisters #illridewithyou."
Ozge Sevindik, whose Twitter profile shows her wearing a hijab, wrote: "I was going to drive to work tomorrow but seeing the outpouring of support changed my mind. #illridewithyou Thank you. See you on the train!"