The prime minister has said lessons will be learned after a whistleblower at the region's ambulance trust exposed 40 alleged cases of harm or deaths due to ambulance delays.
Labour leader Jeremy Corbyn spoke of the damning dossier revealed last week, where a senior staff member in the trust said 19 people died and a further 21 were harmed in less than three weeks between mid-December and early January.
And they estimated by the time investigations finished as many as 80 cases could be recorded.
Mr Corbyn, speaking at prime minister's questions today (Wednesday), said: 'According to a whistleblower as many as 80 patients were harmed or died following significant ambulance delays over a three week period this winter. This is a very serious situation, what investigation is the Department of Health carrying out into these deeply alarming reports?'
Mrs May said investigations would be carried out and 'if there are lessons to be learned, they will be learned'.
MORE: 'Risk summit' ordered after whistleblower raises concerns about East of England Ambulance Service patient deathsShe added: 'When we hear reporters of that sort of course they are very alarming. '
Mr Corbyn also used the example highlighted by the whistleblower of a man in Lowestoft apparently freezing to death after waiting for an ambulance as a example of the 'NHS in crisis'.
However the prime minister said the NHS had been better prepared for winter than ever before.
Peter Aldous, the Conservative MP for Waveney, called on Mrs May to endorse his plea for a 'full and independent investigation' into the case.
He said he had spoken to the person who made the initial call to 999 and had concerns about the process.
MORE: Region's ambulance service could need 120 more staff and 20 extra vehicles, senior manager saysThe region's NHS came under intense pressure between mid-December and early January.
East of England Ambulance Trust said last week: 'We are aware of the claims made by MPs but note no complaints have been received from patients or their families at this time. Nor have any concerns been expressed internally through our line management, whistleblowing or freedom to speak up processes.'
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