UPDATE III: New York Times has a map of where the explosions were.
Authorities will brief reporters at 4:30 ET at the Westin.
UPDATE II: From the AP Twitter: “BREAKING: Intelligence official: 2 more explosive devices found at Boston Marathon; being dismantled”
UPDATE: Two dead, 20-plus wounded according to Boston police.
Fox is reporting at least three dead.
Multiple outlets reporting injuries — as few as six to as many as 50.
There are unconfirmed reports of other “devices,” including in front of the nearby Mandarin Hotel.
A horrific video of one of the explosions as it happened, and a very gruesome picture of the aftermath after the jump. Discretion advised.