WASHINGTON, Jan. 16 (Xinhua) -- The number of Americans without health insurance rose by 1.3 percentage points, or about 3.2 million people in the year of 2017, according to a Gallup survey released Tuesday.

The data represent the country's largest single-year increase since the coverage expansion of the Affordable Care Act, also known as Obamacare which was signed into law by then U.S. president Barack Obama in 2009.

Among those who saw the biggest declines in coverage were people aged from 18 to 25, as well as black and Hispanic people and individuals with an annual household income of less than 36,000 dollars, the Gallup-Sharecare Well-being Index shows.

Despite the hike in 2017, the percentage of Americans without insurance is still low compared to its peak of 18 percent in the third quarter of 2013. The Obamacare's individual mandate, which required people to purchase health insurance or pay a penalty, took effect in the fourth quarter of that year.

Between then and 2016, the number of adults who purchased their own coverage went up 3.7 percent, according to Gallup.

U.S. President Donald Trump signed a major tax bill at the end of last month, repealing the individual mandate under the Obamacare.

The Gallup survey is conducted via phone interviews with 25,072 U.S. adults between Oct. 1 and Dec. 31 in 2017, with an error margin of 1 percentage point.