Pedestrians hold their breath as a vehicle drives past at Hong Kong's Causeway Bay business district March 29. Choking smog enveloped Hong Kong for a second day on Wednesday and the territory's observatory urged people with respiratory problems to cut back on physical exertion and their time outdoors. In the business districts of Central and Causeway Bay, air pollution had shot up to 167 and 157, respectively, on the air pollution index by dawn on Wednesday, levels which the Hong Kong Observatory said were "very high".

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