IT WAS a frantic phone call from the United States that set Gold Coast student and Canadian national Mars Mirza into panic this morning.

Her friend Mel Witcker was in the hospital with a fractured ankle and cuts and abrasions to her legs.

The fit Boston woman had just survived the two bombs detonated at the finish line of the Boston Marathon.

"She was really shook up," Miss Mirza told My Daily News.

"She was crying on the phone."

The marathon runner was coming up to the finishing line when the bombs exploded.

She told Miss Mirza she couldn't see anything other than smoke and people being thrown into the air.

"She said she didn't know if it was the blast that threw people or if it was the stampede of everyone running away," Miss Mirza said.

"Mel's a pretty small girl."

The woman felt the vibrations from the bomb blast and it was enough to knock her and the people around her to the ground.

Another person landed on top of Miss Witcker.

Miss Mirza said her and Miss Witcker became close when she was on student exchange from North-eastern University to Bond University in September last year.

"We were really close," she said.

"I'll never understand why that would be a target."

She said the effects of this bombing would go deeper than just injuries on the surface.

"All those people who didn't have health coverage," she said.

"Mel said she wants to leave the States and move to Canada or back to Australia."

US president Barack Obama said those responsible for the Boston Marathon bombings would feel the 'full weight of justice' after two people were killed and more than 60 injured in the blasts.

The explosions occurred just before 3pm (5am AEST).

TV footage showed two explosions as competitors crossed the finishing line.

Authorities detonated two other explosive devices which were found nearby.