WASHINGTON - President Barack Obama on Wednesday vowed unwavering support to help Haiti recover from a devastating earthquake.

Obama said he had ordered the U.S. government to provide fast, coordinated help to save lives, saying military overflights had already begun assessing damage, emergency supplies were being sent and search and rescue teams would be arriving on Wednesday and Thursday.

This morning I want to extend to the people of Haiti the deep condolences and unwavering support of the American people following yesterday's terrible earthquake, Obama told reporters a 7.0 quake rocked Haiti, killing possibly thousands of people.

We are just now beginning to learn the extent of the devastation, but the reports and images that we've seen of collapsed hospitals, crumbled homes and men and women carrying their injured neighbors through the streets are truly heart-wrenching, he said.

I have directed my administration to respond with a swift, coordinated and aggressive effort to save lives, Obama said.

The people of Haiti will have the full support of the United States in the urgent effort to rescue those trapped beneath the rubble and to deliver the humanitarian relief -- the food, water and medicine -- that Haitians will need in the coming days, he said.

Obama said among the most urgent U.S. priorities was the safety of U.S. diplomats and citizens in Haiti, which U.S. government geologists said had suffered its most powerful quake in more than 200 years.

We're working quickly to account for U.S. embassy personnel and their families in Port-au-Prince, as well as the many American citizens who live and work in Haiti.

(Editing by Sandra Maler)