Paul Rowen, who has promised a full inquiry into the incident, said initial information was that the boy, who is believed to have drowned, was with a party from a children's home which apparently ignored instructions from the two social workers in charge.
The boy, along with four other boys and a girl aged between 13 and 15, had been given permission to go to the Pleasure Beach and was told to meet his supervisors back at their minibus at 9.30pm. Instead, the party apparently wandered along to the promenade. The boy then ignored warning signs and climbed over a chained gate on to a concrete slipway, from where he was swept into the sea.
Mr Rowen said the two staff had acted 'in the manner of reasonable parents' in allowing the party, which was on a day trip to the seaside, some freedom of movement.
Ian Davey, Rochdale's director of social services, said in a statement: 'On the face of it this appears to have been a tragic accident of the kind which must be the nightmare of every parent who has ever taken a youngster to the seaside.
'However, I am unable to make any further comment until there has been a full investigation to see just how this happened.'
Chief Insp Ted Rhodes of Blackpool police said the indications were that the boy was playing a game which involved dodging waves. He was knocked down by one wave then swept away by another. 'The green algae on sections of the slipway nearer the sea makes it extremely slippery when it gets wet,' he said.
He added that the weather had been 'particularly foul' on the night of the incident, and visibility had been poor.
One passer-by dived in after the boy, but was twice thrown back on to some concrete steps by the force of the waves. The police were last night still searching for the boy along a 10-mile stretch of Lancashire coast.