Family, friends and colleagues are remembering NDP Leader Jack Layton as news starts to sink in that the politician known for his warmth and personality has died.

Friends and political foes alike praised Layton on Monday for his warmth, optimism and respect for opponents.

People who squared off politically against Layton, including former prime ministers Jean Chrétien and Paul Martin, as well as Prime Minister Stephen Harper and interim Liberal Leader Bob Rae, all spoke warmly about the NDP leader's commitment to Canadians.

Layton, who led Canada's Official Opposition, died early Monday morning at his Toronto home after a battle with cancer. He was 61.

Layton's wife, Olivia Chow, and his children, Sarah and Michael Layton, issued a statement announcing his death.

"We deeply regret to inform you that the Honourable Jack Layton, leader of the New Democratic Party of Canada, passed away at 4:45 am today, Monday August 22. He passed away peacefully at his home surrounded by family and loved ones," the statement read.

State funeral Saturday

Layton will be honoured with a state funeral Saturday in Toronto, senior NDP officials have told CBC News.

The government protocol office is working with the NDP and family of the NDP leader on exactly what the funeral will be.

Condolence books will be set up in Ottawa on Parliament Hill and in Toronto at city hall. Others will be located in NDP constituency offices across the country.

On Monday, mourners, many bearing flowers and other tributes, arrived at Layton's Toronto constituency office. Friends and areas residents also arrived at his home on the quiet side street where he lived with Chow.

Social media was used to quickly organize public tributes, including gatherings on Parliament Hill, and a rally in Toronto. Later Monday evening, several hundred people came together for a vigil outside the Vancouver Art Gallery.

On Monday evening, hundreds of people were near the Centennial Flame at Parliament Hill, many leaving flowers, cans of Orange Crush that symbolize the NDP's official colour, and notes. The crowd, many bearing candles, sang O Canada as the sun set.

The family released a letter from Layton to Canadians just after noon.

Layton had been battling new cancer

Layton's death comes less than a month after he announced to the country that he was fighting a new form of cancer and was taking time off for treatment. Layton had been diagnosed with prostate cancer in late 2009 and underwent treatment for it. He continued working throughout that time and also battled a broken hip earlier this year. Layton used a cane for much of his time on the campaign trail this spring as he led the NDP to a historic victory on May 2.

His party claimed 103 seats, and was propelled to official Opposition status. Layton and his party were getting used to their new roles in Parliament but he did not appear to be in good health near the end of June. He said he felt pain and stiffness, he underwent tests and they confirmed he had a new form of cancer. He did not disclose what kind of cancer.

Layton's chief of staff, Anne McGrath, said Monday that Layton's condition took a quick turn for the worse Sunday night.

She spent a few hours with him Saturday and had a sense that he was losing a battle, but says his campaign slogan – don't let them tell you it can't be done – was also a personal slogan.

"It is a huge loss. It is a huge loss for me personally, but it's a huge loss also for our party and our country," she said.

McGrath worked with Layton for nearly a decade.

"There's no question that my heart is broken," she said.

McGrath said Layton was thinking about what it would mean for the party if he died. When they spoke on Saturday, they talked about upcoming events like the party's annual caucus retreat in September and what Parliament would be like if he weren't there.

Layton always liked to be presented with options, McGrath told Evan Solomon on CBC's Power & Politics, including a plan for what would happen if he died.

"He was very, very practical and he was very much wanting to know that we were going to be able to continue and we were going to be strong," she said.

After the news of Layton's death emerged shortly after 8 a.m. ET, friends, colleagues and Canadians reacted quickly and with shock, sadness and tears. The flag on the Peace Tower was lowered to half-mast.

Harper saddened by news

Layton's last letter "My friends, love is better than anger. Hope is better than fear. Optimism is better than despair. So let us be loving, hopeful and optimistic. And we'll change the world," Jack Layton writes just days before his death. Read more

Prime Minister Stephen Harper said Layton will be remembered for the force of his personality and his dedication to public life.

Speaking from the foyer of the House of Commons, Harper said the two leaders had always talked about getting together to jam.

"I will always regret the jam session that never was. That is a reminder, I think, that we must always make time for friends, family and loved ones, while we still can," he said.

In a statement earlier Monday, Harper saluted Layton's contribution to public life and said it would be sorely missed.

"I know one thing: Jack gave his fight against cancer everything he had. Indeed, Jack never backed down from any fight," he said.

Tributes to Layton poured in from across party lines. Rae said the news took his breath away and that Layton's death is not just a loss for the NDP, but for all Canadians.

"It's a loss for the country because he was a political guy who believed strongly in politics and who had a lot of resilience and a lot of guts," Rae told CBC News.

NDP colleagues shocked

Longtime NDP leader and MP Ed Broadbent told CBC News he sensed the end was coming, but was still shocked when he got the call Monday morning.

"In each and every election, he moved us forward ... he wanted a reason in politics," Broadbent said.

"Canada has lost a great politician. A man who believed in working for the public good. And I've lost a personal friend."

Interim NDP Leader Nycole Turmel spoke of one of Layton's favourite quotes from Tommy Douglas, the founder of the CCF, the NDP's forerunner. Layton included the quote in every email he sent: "Courage my friends, ‘tis never too late to build a better world."

"Jack was a courageous man. It was his leadership that inspired me, and so many others, to run for office," Turmel said in her statement.

"We – members of Parliament, New Democrats and Canadians – need to pull together now and carry on his fight to make this country a better place."

[IMAGEGALLERY galleryid=1001 size= small] NDP deputy leader Libby Davies, fighting back tears, said Layton's death is "an incredible loss."

"Jack was not only a great leader of the NDP, he's someone that Canadians across the country came to love. We feel a tremendous sense of loss and grief," she said.

Davies said Layton brought a sense of humanity to Canadian politics and in his career and his life, especially his battle with cancer, "he gave it his all."

"We have only love and respect for everything that he did and he leaves some really important legacies in Canadian politics," she said.

The NDP appointed Turmel to take over for Layton temporarily. Layton wanted to be back at work in time for Parliament's fall session in mid-September.

Jack Layton, speaking at the NDP's 50th anniversary convention in June, led his party past the Liberals to become the Official Opposition during the spring election. (Darryl Dyck/Canadian Press) Douglas' daughter, Shirley, says Layton was the same whether he was in a crowded room or meeting people one-on-one.

"Everywhere I've gone, people said 'You know, we've got a leader who cared'," she told CBC News.

Douglas says she's worried about Chow.

"That's the one person I keep thinking about all morning," she said. "They were so close and when a marriage that is as close as that one ... it's a terrible thing to see that marriage broken apart by this. I just couldn't say enough to her. She's a tremendous woman on her own."

The leader of the Official Opposition announced on July 25 he was stepping away from the job to concentrate on his cancer treatment. He told Canadians he had recently been diagnosed with a new form of cancer, in addition to the prostate cancer he had earlier battled.