Former president Ronald Reagan died at his California home this afternoon after taking a turn for the worse in his decade-long battle with Alzheimer's disease. He was 93, the longest-surviving former president in U.S. history.

His wife, Nancy Reagan, and family members had gathered at his house in the Bel Air neighborhood of Los Angeles as Reagan's health deteriorated. He reportedly had slipped into unconsciousness and had been suffering from pneumonia, in addition to Alzheimer's, an incurable disease that destroys brain cells and brings on dementia.

A Reagan family friend said the family was making funeral arrangements and planned to issue a formal statement later, news agencies reported.

President Bush was notified of the death by White House chief of staff Andrew Card during a visit to Paris, where Bush held talks with French President Jacques Chirac on the eve of a trip to Normandy to mark the 60th anniversary of the D-Day landings. A White House spokeswoman said Card learned of the death from Fred Ryan, Reagan's former California chief of staff.

"This is a sad day for America," Bush said when he first heard the news, a presidential aide told reporters.

Later, in a statement he read before reporters at the U.S. ambassador's residence in Paris, Bush said he had telephoned Nancy Reagan to offer her and the Reagan family condolences on behalf of the nation.

"A great American life has come to an end," Bush said. "Ronald Reagan won America's respect with his greatness, and won its love with his goodness. He had the confidence that comes with conviction, the strength that comes with character, the grace that comes with humility, and the humor that comes with wisdom. He leaves behind a nation he restored and a world he helped save."

Blinking back tears, Bush added: "He always told us that for America, the best was yet to come. We comfort ourselves in the knowledge that this is true for him, too. His work is done. And now a shining city awaits him."

Bush referred to one of Reagan's most famous sayings, in which he likened America to "a shining city on a hill."

In Washington, the U.S. flag at the White House was immediately lowered to half-staff.

According to a senior U.S. official accompanying Bush, the president regarded Reagan as a presidential role model. The official said Bush has tried to emulate Reagan's dedication to leadership by conviction and principle and his practice of articulating a broad vision and sticking to it.

Reagan announced publicly in November 1994, five years after leaving office, that he had been diagnosed with Alzheimer's. He said then that he had begun a "journey that will lead me into the sunset of my life," and he vowed not to make any more public appearances.

Nancy Reagan, 81, sought to protect her husband's privacy and declined to disclose details of his condition as his health deteriorated. But she let it be known that he had lost his mental awareness, saying publicly last month, "Ronnie's long journey has finally taken him to a distant place where I can no longer reach him."

Reagan is survived by three children: Michael, from his first marriage, and Patti Davis and Ron from his second, to the former Nancy Davis. Reagan's oldest daughter, Maureen, from his first marriage, died of cancer in August 2001 at age 60.

In a statement, Michael Reagan said, "I pray that as America reflects on the passing of my Dad, they will remember a man of integrity, conviction and good humor that changed America and the world for the better. He would modestly say the credit goes to others, but I believe the credit is his."

Michael Reagan said his father "was always there for me when I needed him" and "played an important role in pointing me to God."

The death reportedly came shortly after 1 p.m. in California (4 p.m. EDT). News agencies and television news networks reported that Reagan's body would be taken shortly to a funeral home in Santa Monica, Calif., then would be brought to his presidential library and museum in Simi Valley, Calif. Plans were being made to fly his body to Washington to lie in state in the Capitol Rotunda, with a state funeral at the National Cathedral, wire services reported. The body then is expected to be returned to California for burial on the grounds of his library.

When he defeated Jimmy Carter in the 1980 election, Reagan -- then 69 -- was the oldest man ever elected president. When he left office in 1989 after two terms, his popularity rating was the highest ever recorded by opinion polls for any retiring president.

As the family made funeral arrangements, tributes to Reagan poured in from around the nation and the world.

Former British prime minister Margaret Thatcher said, "Ronald Reagan had a higher claim than any other leader to have won the Cold War for liberty, and he did it without a shot being fired. She called him "one of my closest political and dearest personal friends."

Thatcher added, "To have achieved so much against so many odds and with such humor and humanity made Ronald Reagan a truly great American hero." She said he will be missed not only by those who knew him and the nation he loved, "but also by millions of men and women who live in freedom today because of the policies he pursued."

French President Chirac called Reagan "a great statesman who through the strength of his convictions and his commitment to democracy will leave a deep mark in history."

Former president Bill Clinton and Sen. Hillary Rodham Clinton (D-N.Y.) said in a statement that Reagan "demonstrated his strength and resolve after leaving office when he shared his struggle with Alzheimer's disease with the world."

California Gov. Arnold Schwarzenegger said he was fortunate to have met Reagan. "He was a great American patriot," Schwarzenegger said. "He was a hero to me."

Sen. John F. Kerry of Massachusetts, the Democratic Party's presumptive presidential nominee, said in a statement, "Ronald Reagan's love of country was infectious. Even when he was breaking Democrats' hearts, he did so with a smile and in the spirit of honest and open debate."

Kerry said of Reagan, "He was the voice of America in good times and in grief. When we lost the brave astronauts in the Challenger tragedy, he reminded us that, 'Nothing ends here; our hopes and our journeys continue.' Now, his own journey has ended -- a long and storied trip that spanned most of the American century and shaped one of the greatest victories of freedom. Today in the face of new challenges, his example reminds us that we must move forward with optimism and resolve. He was our oldest president, but he made America young again."