UPDATE: Justin posted a photo from the hospital and shared a status update.

Original story:

What is going on today? Kelly Osbourne reportedly had a seizure, and Justin Bieber supposedly collapsed at his London concert.

According to TMZ, Justin felt woozy during the show, and with four songs to go he stumbled backstage where he collapsed. According to E! News, JB had told the crowd he wasn't feeling well — he apparently had trouble breathing — and went backstage to get checked out.

According to E!, Justin returned to the stage 10 minutes later and finished the show, despite a doctor reportedly telling him to stop. His manager, Scooter Braun, told the crowd Justin had been "very low of breath" throughout the whole show and was backstage with EMTs. "He got oxygen from emergency personnel. He insisted on finishing the show," his rep told E! "He is on the way to the hospital right now." 

Maybe this explains the gas mask? Weirdly enough, back in November 2011, there was a rumor that Justin had an asthma attack, collapsed, and was hospitalized. That report was deemed false, but it sounds a lot like this one.

Anyway, we hope Justin has a swift recovery!

Sources: E! News, TMZ