Glenys Watson, who works at a cafe on the same road as the school, said the scene was "like a war zone".
"I've never seen so many police cars," she told the BBC.
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Through the day, most of the cloud should break up to leave fine conditions for many with spells of sunshine.
The Eiffel Tower in Paris was plunged into darkness, with the Burj Khalifa in Dubia emblazoned with the Union Jack.
The major party leaders' campaigns for the General Election will remain suspended on Wednesday following the Manchester terror attack.