Grieving friends and top officials gathered in the Northern Irish city of Londonderry for a vigil to honour a 29-year-old journalist who was shot dead during a riot.

Key points: McKee's death has been condemned by Irish Catholic nationalist and pro-British Protestant unionist politicians

McKee's death has been condemned by Irish Catholic nationalist and pro-British Protestant unionist politicians Police believe she was killed by Irish nationalist militants

Police believe she was killed by Irish nationalist militants McKee's partner said her legacy would live on

Lyra McKee was killed on Thursday (local time) by a gunman shooting in the direction of police officers, shortly after she tweeted a photo of a police vehicle being pelted by petrol bombs, with the caption: "Derry tonight. Absolute madness."

Rioting hit the Irish nationalist Creggan area late on Thursday (local time) after a raid by police, who said they were trying to prevent militant attacks during the Easter weekend.

At least 50 petrol bombs were thrown and two cars were set on fire.

A screenshot of a tweet uploaded by Lyra McKee shortly before she attended the scene of the riots. ( Supplied )

The attack, which shocked the region, was likely the work of Irish nationalist militants opposed to the 1998 Good Friday peace deal, police said.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 11 seconds 1 m 11 s Irish police believe militant nationalists are responsible for violence

Addressing crowds gathered in the Creggan area, McKee's partner, Sara Canning, said she had been planning to grow old with a woman whose hopes, dreams and amazing potential were "snuffed out in a single barbaric act".

"The senseless murder of Lyra McKee has left a family without a beloved daughter, a sister, an aunt and a great-aunt; has left so many friends without their confidante. Victims in the LGBTQIA community are left without a tireless advocate and activist, and it's left me without the love of my life, the woman that I was planning to grow old with. We are all poorer for the loss of Lyra. Our hopes and dreams and all her amazing potential were snuffed out in a single barbaric act. This cannot stand. Lyra's death must not be in vain, because her life was a shining light in everyone else's life, and her legacy will live on in the life that she's left behind."

Flowers have been left at the scene where McKee was shot dead. ( Reuters: Clodagh Kilcoyne )

'An inspiring thinker and journalist'

A year after moving to Londonderry, the celebrated young journalist had written about how she looked forward to "better times ahead and saying goodbye to bombs and bullets once and for all".

But just three months later she was killed during a riot that underscored the challenges still faced by Northern Ireland, 21 years after the Good Friday Agreement largely ended decades of deadly sectarian bloodshed.

Born in Belfast just a few years before the 1998 accord was struck to end the kind of violence that took her life, McKee was remembered in an outpouring of tributes as an intelligent, talented writer who brought a human touch to difficult subjects.

In January, she described Londonderry as a beautiful city she had fallen in love with while "falling in love with a woman who hails from it".

McKee wrote and spoke openly about the struggles of growing up gay in a hostile environment.

A 2014 blog post — A Letter To My 14-Year-Old Self — received much acclaim and was subsequently turned into a short film.

McKee was writing a book on the disappearance of young people during the three decades of sectarian violence in Northern Ireland. ( AP: Supplied/McKee family )

In 2006 McKee was awarded Sky News Young Journalist of the Year and was named as one of the "30 under 30 in media" by Forbes Magazine 10 years later.

She wrote for publications both in Northern Ireland and aboard, including the Independent newspaper, the Atlantic and BuzzFeed News.

A "Good Friday baby", McKee was a journalist of courage, style and integrity, said Seamus Dooley, the head of the National Union of Journalists Ireland.

In 2018 McKee signed a two-book deal with British publisher Faber and Faber.

She was writing a book on the disappearance of young people during the British province's three decades of Protestant-Catholic violence that the 1998 deal largely ended.

"She was an inspiring thinker and journalist," Irish Deputy Prime Minister Simon Coveney wrote on Twitter.

He linked his post to a video of a TED talk McKee gave in 2017 encouraging churchgoers and fellow lesbian, gay, bisexual or transgender young people to talk to one another to try and change religious teaching on the subject.

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The death of McKee, who was described by her publisher Faber as a rising star of investigative journalism, was condemned by both Irish Catholic nationalist and pro-British Protestant unionist politicians.

Sinn Fein leader Mary Lou McDonald, holding a rainbow LGBT flag, said: "I carry this flag for Lyra, an activist, a journalist, a child of the peace process, and a woman who should not have lost her life at the age of 29."

Democratic Unionist Party (DUP) leader Arlene Foster said: "When people come out with guns to shoot people from their own community, then we have to say enough is enough."

ABC/Reuters