At least two were dead, 28 injured in two explosions taking place near the Boston Marathon finish line on Monday afternoon, media here reported.

President Barack Obama has been notified of the incident in Boston, a White House official told White House pool media.

Obama directed his administration to provide whatever assistance necessary in the investigation and response, said the official.

Intelligence officials said two more explosive devices have been found at Boston Marathon before being dismantled, media here reported.

The organizers of the Boston Marathon said on Facebook page that bombs caused the two explosions.

The Boston police bomb squad were sweeping the area for suspicious packages, ABC reported. Law enforcement authorities also told ABC they were testing smoke and materials at the scene for chemical substances.

The two explosions happened at around 3 p.m. and went off within seconds of each other. The first runners in the marathon crossed the finish line around noon.

The Boston Police Department said two explosions happened on the Boyleston street near the finish line. Local police, fire and bomb squad have arrived at the scene responding to the incident.

A photographer with Fox affiliate WFXT reported a number of victims with lost limbs.

CNN's video showed heavy smoke on the street, while emergency crews were treating the injured. Bleeding spectators were seen being carried to the medical tent set up to care for the runners.

Many of the injured appeared to be spectators who had gathered at the scene, local media WCVB.com reported. The area has been evacuated.

Police in New York and Washington D.C. have also beefed up security around the cities in the wake of explosions.