More than a million children regularly go to bed hungry in the US, according to a government report that shows a startling increase in the number of families struggling to put food on the table.

President Barack Obama, who pledged to eradicate childhood hunger, has described as "unsettling" the agriculture department survey, which says 50 million people in the US – one in six of the population – were unable to afford to buy sufficient food to stay healthy at some point last year, in large part because of escalating unemployment or poorly paid jobs. That is a rise of more than one-third on the year before and the highest number since the survey began in 1995.

The agriculture secretary, Tom Vilsack, said: "These numbers are a wake-up call … for us to get very serious about food security and hunger, about nutrition and food safety in this country."

Vilsack said he expected the numbers to worsen when the survey for this year is released in 2010.

The report said 6.7 million people were defined as having "very low food security" because they regularly lacked sufficient to eat. Among them, 96% reported that the food they bought did not last until they had money to buy more. Nearly all said they could not afford to eat balanced meals. Although few reported that this was a permanent situation throughout the year, 88% said it had occurred in three or more months.

Nearly half reported losing weight because they did not have enough money to buy food.

The number of children living in households where there were shortages of food at times rose by nearly one-third to 17 million. The report says that most parents who did not get enough to eat ensured their offspring received sufficient food but that more than 1 million children still suffered outright hunger.

The worst affected states are in the south with Mississippi having the largest proportion of its population enduring shortages of food followed by Texas and Arkansas. More than half of those affected are minorities, principally black people and Hispanics.

Millions more Americans do not go hungry only because they are so poor they receive government food stamps or rely on handouts from food banks such as Feeding America. In some states, such as West Virginia, one in six of the population is on food stamps.

Vicki Escarra, head of Feeding America which runs 200 food banks across the country feeding 25 million people, described the report as "alarming" and noted that the situation is continuing to deteriorate.

"Although these new numbers are staggering, it should be noted that these numbers reflect the state of the nation one year ago, in 2008. Since then the economy has significantly weakened, and there are likely many more people struggling with hunger than this report states," she said.

Feeding America said there had been a "dramatic increase" in requests for emergency food assistance from food banks across the US. It said that food banks in some parts of the country were requesting more than a 50% increase in assistance than over a year ago.

"Our network food banks are calling us every day, telling us that demand for emergency food is higher than it has ever been in our history," said Escarra.

The principal cause is unemployment, which has risen past 10%, as well as increasing numbers of people who have had their hours cut back or been forced in to minimum wage jobs. Even before the recent economic collapse many working people were struggling to meet rising living costs, such as those who drive long distances to their jobs in rural states who were hit by the rising cost of fuel.

Feeding America said 40%of the people it helps live in families with at least one working adult.

Charities say that many of those who fall into financial difficulties take years to get back on their feet and so the problem is likely to persist for years.

The report comes as the United Nations holds a summit in Rome on food security. The UN secretary general, Ban Ki-moon, told the summit that a child dies of hunger every five seconds somewhere in the world and that more than 1 billion live with hunger.