Beijing's API today is at 307, corresponding to a PM10 concentration of 426 ug/m3. The US EPA calls this "Hazardous - Health warnings of emergency conditions. The entire population is more likely to be affected." China, on the other hand, merely calls it 重污染, heavy pollution.
I wonder if this is related to the Mandarin Oriental fire?
Image: The Beijinger
Another recommended link about the fire:
Much more info about China and US API designations in this related post:
12/9/08: stay inside today - beijing api at 246