The bustling Co Tyrone town was filled with shoppers, both locals and visitors alike, when a bomb warning was telephoned to UTV and passed to police.
But with the caller giving the wrong location of the reported device, attempts to evacuate the area saw many people unwittingly steered directly into the path of danger.
Shortly after 3pm on Saturday 15 August 1998, the bomb exploded in the Market Street area.
Eye witnesses and first responders were stunned by the extent of the devastation, as both the death toll and the number of people in critical conditions rose.
"It was just a battlefield ... Scores of injured, people screaming," Paddy McGowan, an independent councillor who had been a fire officer for many years during the Troubles, said at the time.
People were asking for help and there was nothing you could do – you just felt helpless.
Nine children and three generations of one family - including a woman pregnant with twins - were among the 29 killed. Over 200 more were injured, many seriously.
The Omagh atrocity, found to have been caused by a massive 500lb car-bomb planted by the Real IRA, was to be the single biggest loss of life of the Troubles.
Chilling pictures would later show that, earlier in the day, people had walked past the maroon Vauxhall Astra in which the device had been placed - unaware of what lay ahead.
The bombing came four years after the ceasefire called by the Provisional IRA and just four months after the signing of the Good Friday Agreement.
Messages of sympathy were sent from the Queen, then US President Bill Clinton and the Pope, while leaders of the four main churches in Northern Ireland united to speak out against the attack.
Politicians from across party divides would also be unanimous in both their condemnation of the atrocity and their determination to find a way forward for a place still striving for peace.
Those who lost their lives were James Barker (12) from Buncrana, Fernando Blasco Baselga (12) from Madrid, Geraldine Breslin (43) from Omagh, Deborah Anne Cartwright (20) from Omagh, Gareth Conway (18) from Carrickmore, Breda Devine (20 months) from Donemana, Oran Doherty (8) from Buncrana, Aidan Gallagher (21) from Omagh, Esther Gibson (36) from Beragh, Mary Grimes (65) from Beragh, Olive Hawkes (60) from Omagh, Julia Hughes (21) Omagh, Brenda Logue (17) from Omagh, Anne McCombe (45) from Omagh, Brian McCrory (54) from Omagh, Samantha McFarland (17) Omagh, Seán McGrath (61) from Omagh, Sean McLaughlin (12) from Buncrana, Jolene Marlow (17) Omagh, Avril Monaghan (30) from Augher, Maura Monaghan (18 months) from Augher, Alan Radford (16) Omagh, Rocio Abad Ramos (23) from Madrid, Elizabeth Rush (57) Omagh, Veda Short (46) from Omagh,Philomena Skelton (39) from Durmquin, Frederick White (60) from Omagh, Bryan White (26) from Omagh, Lorraine Wilson (15) Omagh.
Omagh: In Words
I can barely express the sense of grief I feel for the victims of this appalling, evil act of savagery.
- Prime Minister Tony Blair
Our hearts go out to all those relatives. It is a ghastly act, and a cruel act.
- Taoiseach Bertie Ahern
Everything was torn asunder by a barbarous act.
- John McFall, NIO Minister
The hopes and dreams of so many families have been obliterated in a cruel afternoon.
- Irish President Mary McAleese
I saw grown men crying; men in their uniforms covered in blood ... The people of Omagh have had a terrible price to pay.
- Seamus Mallon, deputy First Minister
I am totally horrified by this action. I condemn it without any equivocation whatsoever.
- Sinn Féin President Gerry Adams
I believe it was intended that society would suffer - so that the distrust between the traditions would be built up and the way in which we'd hoped to move forward would be disrupted. That's something we've got to resist.
- Ken Maginness, UUP MP
They've left so many homes broken, hearts broken ...
Willie McCrea, DUP MP
We've had men, women and children slaughtered here - slaughtered by murderers who wanted to murder, slaughtered by murderers who have nothing else to offer but murder.
- RUC Chief Constable Ronnie Flanagan
Even if they are never put in prison, the people who planned and carried this out will be prisoners for the rest of their lives. They will have to live with what they have done inside their heads. They will never escape that.
- Michael Gallagher, father of victim Aidan
A memorial to the victims of the 1998 Omagh bomb attack.