The city of Joplin in the US state of Missouri has observed a moment's silence to remember the time exactly one week ago a devastating tornado struck, killing at least 142 people.
Residents stood silent amid still-uncleared debris at 1741 local time (2241 GMT).
Earlier visiting President Barack Obama pledged he was with Joplin "every step of the way" as it rebuilt.
He toured devastated areas and spoke at a memorial service in the city.
The city of Joplin had urged residents "to stop their activities and pause for a Moment of Silence at 5.41 PM on Sunday, May 29, to honour those who lost their lives or have been injured and are suffering because of this disaster that struck Joplin one week ago."
Hundreds of citizens stood silent amid wreckage in the city's Cunningham Park.
Earlier, Mr Obama had spoken at a memorial service at Missouri Southern State University.
He said: "We will be with you every step of the way. The cameras may leave, the spotlight may shift. But we will be with you every step of the way until Joplin is restored and this community is back on its feet."
He recalled the heroism of pizza manager Christopher Lucas, who held a freezer door open from the outside to save people sheltering within.
"He died saving more than a dozen people in that freezer," Mr Obama said. "You see, there are heroes all around us all the time."
In a speech interrupted by many cheers, he added: "You've demonstrated a simple truth... that amid heartbreak and tragedy no-one is a stranger. Everybody is a brother. Everybody is a sister. We can all love one another."
Mr Obama praised rescue workers.
"Some of you used your pick-up trucks as ambulances, carrying the injured on doors that served as stretchers. Your restaurants have rushed food to people in need. Businesses have filled trucks with donations. You've waited in line for hours to donate blood."
Earlier, Mr Obama drove through the hardest-hit areas with Missouri Governor Jay Nixon, stopping to talk to residents.
He asked Americans to give money to the Red Cross or other organisations to help the relief effort.
His message to those affected: "This is not just your tragedy, it is a national tragedy and there will be a national response."
The BBC's Paul Adams in Washington says this is the third time this year - after the Tuscaloosa tornadoes and Mississippi floods - that Mr Obama has felt the need to be at the scene of natural disasters to reassure the population they will not have to fend for themselves.
'We will heal'
The tornado was one of the most destructive in US history.
With winds of 200mph (322km/h), it carved a swathe of destruction through Joplin, injuring more than 900 people.
Officials say the number of people missing has come down, after many were reported safe, but 43 are still unaccounted for.
Governor Nixon had declared Sunday an official State Day of Prayer and Remembrance.
US and Missouri flags have flown at half-mast over all government buildings in the state throughout the day.
At the memorial service, he said: "The people of Missouri were born for this mission. We are famously stubborn and self-reliant, practical, impatient. No storm, no fire, no flood can turn us from our task.
"We can and we will heal. We've already begun. By God's grace, we will restore this community."
The US National Weather Service says that 2011 is already the deadliest year for tornadoes since 1950, when precise figures were first kept.
The death toll so far this year stands at 520. The previous highest recorded death toll in a single year was 519 in 1953.