Dozens of people injured after explosion at Boston Marathon

A photo of the apparent explosion posted on Twitter (photo via Boston to A T)

Dozens of people have been injured after two reported explosions at the finish line of the Boston Marathon. At least 12 people were seriously injured and transported to local hospitals, according to Boston ABC affiliate WCVB.
The Boston Globe cited witnesses who reported hearing two large explosions shortly before 3pm ET. The Associated Press reported at least one of the explosions came near the entrance of the Fairmont Copley Hotel. Meanwhile, photos posted on Twitter showed several people severely injured along Boylston Street--at the center of the Boston's main shopping district. Local news reporter Jackie Bruno wrote that she saw some people with their limbs blown off.
Phones were not being answered at the Boston Police Department. But scanner traffic indicated police were investigating "several suspect packages" on Boylston Street. Police are evacuating the area. Runners who had not yet finished the race were stopped and are being told to leave the area.
Twitter user Matt Norlinder posted a screenshot of the explosion captured by the local CBS affiliate.