The explosive device was thrown from a passing motorcycle and discharged in the outdoor market, according to the BBC. Bomb disposal experts are defusing a second device on the scene that did not detonate. No one has claimed responsibility for the attack.
One Twitter user based out of the U.S. appeared to be in Cairo at the time and document his reactions to the news.
@Ramblurr: Bomb in Cairo. I'm ok.
@Ramblurr: Wow. I'm safe, but I know 2 people who were at Khan al-khalili .. no word yet. I hope they're ok
@Ramblurr: The internet is slow but, the local Egyptian TV says 4 killed and 12 wounded thus far. Two bombs, one was "safely detonated"
Another user documented his reaction in Cairo and recalled a similar incident four years ago.
@andrewheiss (Cairo, Egypt): Explosion downtown at a cafe near the Khan. We're far away, alhamdulillah
@andrewheiss (Cairo, Egypt): 2nd explosion at the Khan while they were diffusing the bomb. 4 dead now, 18+ injured. Yikes. #Cairo
@andrewheiss (Cairo, Egypt): Just called my home teaching families as part of the branch emergency phone tree. Everyone's okay. #Cairo
@andrewheiss (Cairo, Egypt): This happened four years ago in almost the same spot, across the street at al-Azhar http://bit.ly/117AWQ #Cairo
Other users simply alerted loved ones that they were safe.
@ibrakoor (Cairo, Egypt): :there was a bombing in Cairo 45 minutes ago at Khan al-Khalili. I am safe. I live outside the city. But I go to that area all the time.
@ahmednaguib (Cairo, Egypt): @justlikeanovel we are okay thanks, our home is really far from where the bombings took place so everything is cool.
@markjaffrey (Cairo, Egypt): In case anyone is worried, we were nowhere near the bomb blast in the centre of Cairo this afternoon. We live 8 miles south of the centre.
Another Twitter user claims Egyptian security forces are preventing coverage of the event and provides images (posts in both Arabic and English).
@ircpresident (Egypt): الأمن يمنع المصريين من تغطية الحدث، Security blocks journalists to prevent them from coverage. Http://is.gd/ksFl