Basically, the United flight holds short of runway 28 as he may need a little more time (this is the United flight CNN showed sitting there, probably).

The ATC controller knows something has happened because the first time we hear from 214 heavy, the controller tells the pilot emergency vehicles are on the way.

Then some captains on final announce they're going around and some ask for redirect (one clearly to San Jose). The controller then tells some flights on final to go around.

Finally he's directing rescue units to cross all runways where normally they'd hold at each runway to be directed.

I found these comments helpful. They breakdown the exchange between the tower and the approaching planes. The first is from an air traffic controller.

http://www.reddit.com/r/worldnews/comments/1hrewx/asiana_air...

http://www.reddit.com/r/worldnews/comments/1hrewx/asiana_air...