Victims' families, survivors and emergency services personnel who responded to the blaze on November 18th 1987, gathered at the north London Tube station at 11am.
They came together in the ticket hall where 31 people died and around 60 were injured when a fireball, thought to have been caused by a dropped match, engulfed the wooden escalator leading up from the Piccadilly Line.
London Fire Brigade's Chaplain - the Reverend Deacon Ian Black - took the short service.
He told those gathered: "We pray for the injured and those bereaved by this tragedy.
"As we go our separate ways, we take with us the undying memories of those we loved and are no longer with us."
London Underground managing director Mark Wild also paid tribute to the station staff, train drivers and emergency services who "were very brave".
He added: "The really key thing out of King's Cross is it instilled a safety culture in London Underground of continuously improving.
"Even though that risk has been eliminated, we're always alert to future ones."
Smoking was immediately banned on all parts of the Tube after the disaster, wooden escalators were replaced and Underground staff were trained in what to do in the event of a fire.
Mick Cash, general secretary of the Rail, Maritime and Transport union, said the King's Cross fire stands alongside the disaster at Grenfell Tower as a reminder that "safety and regulation must remain our watchwords regardless of what the bottom line says on a set of accounts".
