CNN is reporting that a pair of explosions went off this afternoon near the finish line of the Boston Marathon, reportedly leaving at least two people dead. Boston police gave an update on the casualties around 4 p.m. ET, saying that at least 23 people had been injured.

Other early reports placed the number of injured higher, with some observers saying “dozens” of people had been hurt. The facts in the incident were still developing, and the numbers were expected to change.

CNN reported on its website: “The blasts occurred a few seconds apart, shrouding downtown Boston’s Copley Square in smoke. Paramedics were treating several victims at the scene, and police ordered onlookers to back away from the area, CNN Producer Matt Frucci reported.”

Some of the injuries have been described by witnesses as severe.

CNN.com adds: “The explosions occurred about 2:45 p.m., about an hour after the first runners had crossed the finish line, Frucci said.”

Cable news channels and the broadcast networks cut to full-time coverage of the chaotic developments in Boston, as did many local TV stations around the country. In Los Angeles almost all of the local stations interrupted their normal programming and remained on the Boston story more than an hour and a half after the incident occurred.

NBC, CBS and ABC brought in their top news personnel and shifted to full-time coverage of the explosions, which were captured on video.

According to some reports, unexploded bombs were found in the area. The blasts were being referred to as a “bombing” by some, including Vice President Joe Biden. However, it was unclear in the immediate aftermath of the explosions whether they might have been accidental.

Nonetheless, security personnel were reportedly on high alert in Boston, with the Massachusetts National Guard called in. Security was also stepped up in New York City, CNN reports.

The FBI was reportedly working with Boston authorities to try to piece together what happened.