TIANJIN - Air and water quality near the site of Wednesday night's blast in north China's Tianjin are being closely monitored as conditions remain unclear.

"So far, the air quality near the blast site remains normal and will not have a harmful effect on residents," Feng Yinchang, an environmental expert, said at a press conference Friday morning.

Some of the monitoring stations detected toluene, chloroform, methylbenzene and volatile organic compounds, all hazardous pollutants, between Wednesday night and noon on Thursday, but their concentrations were decreasing because of wind blowing toward the sea, Feng said.

As of Thursday noon, all toxic gas indicators were within normal range. However, the quality of air and water will continue to be closely monitored, Feng added.

Discharge into the sea was closed on Thursday morning and rainwater drainage pipes were also closed in the afternoon, said Wang Lianqing, a senior engineer with the Tianjin Association of Environmental Protection Industry.

All contaminated water has been contained within a sewage plant, said Wang, and the plant has adopted a biochemical treatment system to process the polluted water.

An expert team was working on-site to assess the best plan, he added.