The house fire that left two women and three children dead was "severe", a spokesman for South Yorkshire Fire and Rescue said.
He said: "Our investigators are arriving here at 9am, so we we will know more later on this morning."
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Rescue workers are at the site Sunday morning trying to cut open mangled coaches.
Despite chilly temperatures it will be a mostly dry day, and milder than yesterday.
The Sunday Times alleges a missile malfunctioned after launch during a routine test of the UK's nuclear deterrent last year.