FBI special agent-in-charge Rick Deslauriers told a media conference that both explosives were placed inside black nylon bags or backpacks.

LIVE UPDATE. ALL TIMES ARE AEST

5.48pm: More than 2000 tips have been received following a public appeal by the FBI to help solve the Boston Marathon bombings.

5.30pm: The Tribeca Film Festival was born out of the 9/11 terror attacks and celebrities attending an annual Vanity Fair gala in New York City to kick off this year's event were mindful of the shadow cast by the explosions at the Boston Marathon.

Two men in hazardous materials suits put numbers on the shattered glass and debris as they investigate the scene at the first bombing.

Police and security guards were visible at the festival on Tuesday night, where there was an outdoor metal detector for arriving guests.

Whoopi Goldberg said she understood if some people were apprehensive about going out in crowded, public areas.

''I say that's alright. We're out for you,'' she said.

''Stay until you feel better. But we're out here and we got your back.''

Fox News has released an image of what appears to be an exploded backpack at the scene of the Boston bombings.

Aida Turturro, best known for her role on TV's The Sopranos, said it's important to live your life and not be scared.

''You never know. I mean you can die by crossing the street or you can get hit by a car. . . . I think the best thing is to continue life because if you don't they're winning,'' she said.

''If they keep you from living your life then they've won. They've taken your life away from you right there.''

5.15pm: A Chinese newspaper has named a person they say is the third victim of the Boston Marathon bombings.

Images from the Department of Homeland Security show improvised explosive devices using pressure cookers.