Joplin, Minneapolis: Face to face with the legions of homeless and the bereaved, President Barack Obama on Sunday toured the apocalyptic landscape left by Missouri's killer tornado, consoled the community and committed the government to helping rebuild shattered lives.

"We're not going to stop 'til Joplin's back on its feet," Obama vowed.

A memorial service where Obama spoke punctuated a day of remembrance one week after the disaster, as authorities pressed on with the task of identifying the victims and volunteers combed through wreckage of neighbourhoods where nothing was left whole.

The service erupted in cheers when Obama said: "I promise you your country will be there with you every single step of the way," a pledge he extended to all parts of the nation raked by violent storms this season.

Before the service, Obama's motorcade pulled into a neighbourhood where downed trees cleaved open houses, roofs were stripped or blown off, cars were cratered and splintered wood was everywhere.

"This is not just your tragedy," Obama said. "This is a national tragedy, and that means there will be a national response."

He added, "We are going to be here long after the cameras leave."

Obama returned to the US on Saturday from a six-day European tour of Ireland, Britain, France and Poland.

After days of focusing on the US relationship with the rest of the world, Sunday was about an even more critical connection: his own, with the American people.

The tornado was the worst in decades, leaving more than 120 dead and hundreds more injured. At least 40 remain unaccounted for.

Tags: missouri tornado, Missouri town, obama missouri tour, tornado Joplin, Tornadoes in Missouri, US tornado, US tornadoes