Chinese Premier Li Keqiang has visited Tianjin, days after the explosions killed at least 114 people and flattened part of a national development zone, state media reported.

Li toured the site of the blasts upon his arrival in Tianjin, where he is set to oversee the search and rescue operation.

China's state broadcaster CCTV said Li stressed the importance of monitoring the quality of the air, water and soil in the area.

Li also visited a local hospital where people injured by explosions were being treated, CCTV said.

He paid his respects to the fire-fighters who lost their lives during the rescue operation, CCTV added. At least 39 fire fighters were killed, according to state media.

The number of missing was estimated at 70, most of them fire fighters, CCTV said, suggesting the death toll would rise further.

Yesterday, Chinese officialsfor the first time confirmed that sodium cyanide, which is fatal when ingested or inhaled, had been found at the site, and east of the site.

Wednesday night's blasts happened at a warehouse containing toxic chemicals.