I have just heard this on my local BBC radio station; its now confirmed on the main BBC webpage. Will update when more news comes through : my heart goes out to those who have been injured, or are in a worse condition.
There has been an explosion in a building in New York.
Fire engines are at the scene and the area has been sealed off, amid reports that there was severe damage.
Witnesses speak of many people being inside the building, which is next door to a technical college.
The explosion is reported to have happened on West 19th Street, between Sixth and Seventh Avenues in Manhattan.
View: BBC Page
Update from cnn.com
The incident happened at Apex Technical School in the Chelsea neighborhood.
Streets in the area around 19th Street and Sixth Avenue were closed to traffic.
At least 21 people, some with cuts visible, were being treated at the scene.
Police, fire and rescue units responded to the blast, and some rubble was visible on the street. But no fire or smoke was evident.
More than 100 firefighters were on the scene, fire officials said.
View: CNN article
As you can see news is still scetchy atm - will update with move comprehensive news as soon as possible.
Update 2
It appears the explosion happened in the building housing the offices and residential units, authorities said, and no foul play was suspected. Authorities said plumbers were working on a boiler in the basement and that "may have had something to do with it."
Students were evacuated from the eight-story Apex Technical School adjoining the building where authorities said the explosion occurred. Streets in the area around 19th Street and Sixth Avenue were closed to traffic.
"I was on 20th Street in the rear of the building and I was literally directly across the street when the explosion happened," said witness John Heffernan. "Two huge windows blew out and glass shattered all around me. I ran underneath an awning and the glass just came down all around me."
"I just ducked because all the glass and flames and fire was coming toward me," said Steve Jaisingh, who works in the basement of the Kaltech building. "If I didn't duck, I would have died."
News source: 
