Local rescue officials and Interior Minister Gerard Collomb had previously said the death toll stood at eight.
Philippe said around 50 people were injured, including three seriously, on St Martin and the nearby smaller island of St Barthelemy. Twenty-one have been hospitalised.
He said officials were in the process of identifying the four dead, adding that no deaths were reported from St Barthelemy.
Hurricane Irma lashes Caribbean, Florida braces for hit
On St Martin, 60 per cent of homes have been damaged so badly that they are uninhabitable, Philippe said, describing the disaster as "unimaginable and unprecedented".
Power is cut across St Martin as well as supplies of potable water and petrol, he said. Roads are either partly or totally impassable, he added.
However the harbour and airport are back in use, he said, noting that a military plane landed on the island Thursday.
"The work will be long, emotions will run deep and the sadness will be great," he said.
One of the most powerful Atlantic storms on record, the rare Category 5 hurricane started its deadly rampage on Wednesday when it made landfall in Barbuda to the southeast.
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