A tourist poses for photos with the Merlion (unseen) in the hazy skyline of Singapore June 20, 2013. Singapore's haze deteriorated to "hazardous" levels late on Wednesday as smoke from slash-and-burn land clearing in Indonesia enveloped the city-state, inflaming tensions between the Southeast Asian neighbours. The Pollution Standards Index (PSI) soared to a record high of 321 at 10 pm, up from 290 just an hour earlier and below 200 earlier in the day. A PSI reading above 300 indicates "hazardous" air quality, while a reading between 201 and 300 means "very unhealthy".[Photo/Agencies]

Construction workers wear face masks, to protect them from a heavy smoke haze, as they perform morning exercises at the start of their shift in Singapore June 20, 2013. Singapore's air quality deteriorated to "hazardous" levels late on Wednesday as smoke from slash-and-burn land clearing in Indonesia enveloped the city-state, inflaming tensions between the Southeast Asian neighbors.[Photo/Agencies]