Update, 5:00 p.m.: The Sun and the local CBS affiliate report the only person injured in the crash was the driver of the tractor trailer. He's been transported to a hospital and is now in serious but stable condition. Also, transportation officials confirmed there were no toxic inhalants on the train. 

Update, 3:07 p.m.: Two men were driving and recording the smoke billowing into the sky when they caught one of the major explosions on video. Warning: there's some not-safe-for-work language used in the video: 

Original: A derailed train just outside the hub of Baltimore sent a huge plume of smoke into the sky Tuesday afternoon that could be seen from downtown, as buildings shook from miles away and residents feared the worst from schools and office buildings across the city. UpdateThe local CBS station reports that a tractor trailer collided with a cargo train around 2 p.m. in the Rosedale area of Baltimore, sending the train off the tracks and into the surrounding area. The Baltimore Sun reports hazardous material teams are on the scene. The Sun is also reporting several buildings collapsed after the explosion happened. 

We first heard about the explosion through the many reports coming in via social media, where rumblings of rumblings erupted on Twitter, as is so often the case, and made their way toward roundups like this Reddit thread. Those efforts led us to these disturbing pictures of the accident: 

This a developing story and we'll update as we learn more. (Updates are at the top of the page.)