Bloomberg, who is a political independent, has in the past criticised both Obama and Republican challenger Mitt Romney for their failure to confront the problems afflicting the nation, including a slow economic recovery and balancing the budget.
However, the billionaire New York mayor voiced support for Obama in the wake of the devastation caused by Sandy, which brought the city to a standstill and resulted in significant loss of life.
"The devastation that Hurricane Sandy brought to New York City and much of the Northeast -- in lost lives, lost homes and lost business -- brought the stakes of Tuesday's presidential election into sharp relief," he wrote in an op-ed column published by Bloomberg News.
Sandy, coming just 14 months after Hurricane Irene pummeled the city, forced evacuation of thousands of people, brought the crucial mass transport system to a grinding halt, left millions without power and caused significant economic damage.
"In just 14 months, two hurricanes have forced us to evacuate neighbourhoods -- something our city government had never done before. If this is a trend, it is simply not sustainable. Our climate is changing. And while the increase in extreme weather we have experienced in New York City and around the world may or may not be the result of it, the risk that it might be -- given this week's devastation -- should compel all elected leaders to take immediate action."
Bloomberg said climate change and its effects cannot be tackled alone and "we need leadership from the White House."
"... And over the past four years, President Barack Obama has taken major steps to reduce our carbon consumption, including setting higher fuel- efficiency standards for cars and trucks. His administration also has adopted tighter controls on mercury emissions, which will help to close the dirtiest coal power plants (an effort I have supported through my philanthropy), which are estimated to kill 13,000 Americans a year."
Bloomberg said while Obama sees climate change as an urgent problem that threatens the planet, Romney does not.
The endorsement by Bloomberg provides a crucial boost to Obama just days ahead of the November 6 presidential election, which promises to be a tightly fought race.
The support by Bloomberg was unexpected, with both the Obama and Romney campaigns seeking the mayor's endorsement, given that he is in a position to influence independent voters around the country.
Bloomberg said if Obama listens to people on "both sides of the aisle, and builds the trust of moderates, he can fulfill the hope he inspired four years ago and lead our country toward a better future for my children and yours. And that's why I will be voting for him."
A lifelong democrat who had turned Republican before becoming an independent, Bloomberg said Romney is a "good and decent man" who as Massachusetts governor had taken important steps to tackle climate change, including signing on to a regional cap-and-trade plan.
The plan was designed to reduce carbon emissions 10 per cent below 1990 levels. However, Bloomberg expressed disappointment that Romney has since "reversed course, abandoning the very cap-and-trade program he once supported"
Among the other reasons cited by Bloomberg for his endorsement of Obama was the president's support for abortion rights and for same-sex couples.
Obama issued a statement welcoming the endorsement and pledged to continue to stand with New York in its time of need.
"While we may not agree on every issue, Mayor Bloomberg and I agree on the most important issues of our time -- that the key to a strong economy is investing in the skills and education of our people, that immigration reform is essential to an open and dynamic democracy, and that climate change is a threat to our children's future, and we owe it to them to do something about it," Obama said.
Bloomberg had not endorsed a presidential candidate in 2008, when Obama ran against Senator John McCain [ Images ]. He had endorsed Republican President George W Bush's [ Images ] re-election in 2004.