The 75-year-old was admitted to the University of California Irvine Medical Centre on Tuesday evening "for a non-COVID-19 infection," Clinton spokesman Angel Urena said on Twitter.

"He is on the mend, in good spirits, and incredibly thankful to the doctors, nurses and staff providing him with excellent care," Urena wrote. The spokesman added to Reuters: "He's up and about, joking and charming the hospital staff."

Clinton went to the hospital after feeling fatigued and was diagnosed with an infection of the bloodstream that doctors believe started as a urinary tract infection, CNN reported, citing his doctors.

The former president's physicians, Alpesh Amin and Lisa Bardack, said he was "admitted to the hospital for close monitoring and administered IV antibiotics and fluids."

"He remains at the hospital for continuous monitoring," they said in a statement. "After two days of treatment, his white blood cell count is trending down and he is responding to antibiotics well."

They added: "We hope to have him go home soon."

CNN cited doctors saying Clinton was in the intensive care unit primarily to give him privacy.

Clinton, a Democrat who was president from 1993-2001, has had past health issues, including a 2004 quadruple bypass surgery and a 2010 procedure to open a blocked artery in his heart with two stents. CNN reported that Clinton's current hospital stay is not related to his heart issues.

The former Arkansas governor came to the White House by defeating an incumbent president, Republican George H.W. Bush, and served during a period of acute partisanship in Washington, a harbinger of the current bitter political state.

Clinton won re-election in 1996 against longtime Republican Senator Bob Dole.

Clinton endured bruising political battles with Republicans. He was impeached in 1998 by the Republican-led House of Representatives over his sexual relationship with White House intern Monica Lewinsky but remained in office when the Senate acquitted him in 1999.

He is known for a remarkable talent for connecting with people and an exceptional understanding of policy issues.

Clinton morphed into a political husband after leaving office, when his wife Hillary Clinton was elected US senator from New York in 2000. She unsuccessfully sought the 2008 Democratic presidential nomination and won the party's 2016 nomination before losing the election to Donald Trump.

Australian Associated Press