NHS Direct has told ITV News they are investigating one "unexpected death" after a patient in the West Midlands contacted its 111 helpline service.
NHS Direct said of the nine contracts it is currently operating, it is investigating seven "potentially serious" incidents related to calls to the 111 service.
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The storms that struck Texas and Oklahoma late on Tuesday brought tornadoes, tennis ball-sized hail and powerful winds.
Samantha Baldwin, 42, and her sons Louis Madge, nine, and Dylan Madge, six, haven't been seen for two days.
A spokesman for the UK Coastguard said it was coordinating a search operation in the Caernarfon Bay area of North Wales.