City's vice-mayor admits the chemical has spread 1km from blast site, amid concerns it will react with rain to produce deadly compound

The explosions in Tianjin last week scattered sodium cyanide as far as 1km from the blast site, the city's vice-mayor admitted on Monday, as fears rose that rain forecast over the next few days could react with the chemical to release highly poisonous hydrogen cyanide gas.

Making his first public appearance since Wednesday's blasts, He Shushan, who is in charge of work safety in the city, explained his absence as due to a desperate attempt to search for and remove the chemical over the past few days.

He played down fears over its presence, saying that military specialists and government staff had twice scoured a 1km radius from the centre of the blast.

The death toll from the disaster rose to 114 on Monday, with 70 still missing, most of them "contract firefighters".

The relatives of some victims said they had been grounded in hotels, to prevent protests.

Authorities have been tight-lipped about the presence of sodium cyanide at the site. The first official confirmation of its existence there came from a Beijing military official on Sunday.