Overnight, Irma was downgraded to a category 2 storm, but continued to wreak havoc along the west coast of Florida.
On Wednesday the Government pledged an additional £25 million to help the rebuilding effort on top of the £32 million already promised.
Following a meeting of the Government's emergency Cobra committee on Saturday, Sir Michael said: "The relief operation is now well under way".
Only approved relief flights are being allowed into the British overseas territory.
"These are British people and we are here for the long term and we will come through with a recovery plan working with our partners in the region".
He goes on: "We can only send this email by sitting outside the phone company office in town".
More than US$1.3 billion of damage has been caused to the British Virgin Islands (BVI).
FOR MANY readers of The Voice, the devastation wreaked by Hurricane Irma across the Caribbean and beyond is deeply personal.
The UK has sent military planes, and on Sunday the Royal Navy said local people had helped a helicopter team empty restorative supplies, including immunizations.
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A British Foreign Officer minister said earlier today that there had been a "serious threat of the complete breakdown of law and order".
Pressed on how he thinks he will be received during the visit by those affected, Mr Johnson said: "Most fair-minded people have said that the United Kingdom responded extremely fast and extremely well".
"We pre-positioned a ship in the Caribbean for the hurricane season", he said.
"We have troops helping at the moment". Meanwhile, roughly 60 percent of Barbuda's population has reportedly been left homeless and almost every building either damaged or demolished.
"We were there as soon as we possibly could".
Chaos still reigned in much of the storm-tossed Caribbean on Monday, as food and water shortages, power outages and rampant looting across several islands sparked angry criticism from residents who demanded more government help.
More than six million people in Florida and Georgia have been warned to leave their homes as the National Hurricane Centre warned the storm will bring "life-threatening" wind, with forecasters predicting storm surges of up to 15 ft.
Water levels are expected to rise between 10-15ft in the areas at risk.
After passing through the Caribbean, Irma travelled north to Florida.