UK national seeking 10 day visa to Beijing last minute

Hello, I found out yesterday that I am needed for a conference in Beijing in five days time. I am currently visiting in Canada and unable to seek it before travelling. Can I get the proper one in Schenzhen? I can get a letter detailing the need beforehand...but am axious to know the best way to have this letter written. What kind do I seek and where in Schenzhen do I go to get it? Any help is appreciated. :-)