The White House issued a release calling for the Federal Emergency Management Agency to coordinate all disaster relief efforts to "alleviate the hardship and suffering" on residents. Flint switched water supplies in 2014, and the corrosive water from the Flint River leached lead from old pipes.
FEMA has been authorized to provide water, filters, cartridges and other items for 90 days. Direct federal funding also will be made available.
Republican Gov. Rick Snyder requested the declaration late Thursday, saying needs "far exceed the state's capability," and added that emergency measures could cost $41 million. His letter to Obama painted a bleak picture of the troubled city, describing Flint as an "impoverished area" that has been overwhelmed by the release of lead from old pipes.
The tap water in Flint, population 99,000, became contaminated after the city switched its water supply from the Detroit water system to the Flint River while a pipeline to Lake Huron is under construction. The corrosive water lacked adequate treatment and caused lead to leach from old pipes in homes and schools.
Flint returned to the Detroit system in October after elevated lead levels were discovered in children, and could tap into the new pipeline by summer.
But officials remain concerned that damaged pipes could continue to leach lead, to which exposure can cause behavior problems and learning disabilities in children as well as kidney ailments in adults.
A spike in cases of Legionnaires' disease may also be tied to the water contamination. CBS News correspondent Adriana Diaz reported Friday there have been 87 cases of the pneumonia-like illness since the water switch -- and ten people have died.
The National Guard began distributing free water, filters and other supplies earlier this week. But for angry residents, it's not enough.
Friday night at Freeman Elementary School's Family Fun Night, health officials conducted lead testing for children, CBS affiliate WWJ reported.
"It really is a scary situation to know that we can't get clean drinking water," said Sherri Miller, who brought her first-grade son, Jameer, to have a finger-prick blood sample tested. "It really is scary to think someone knew about this" and did nothing.
"It has such damning, lifelong and generational consequences," said Dr. Mona Hanna-Attisha, director of pediatric residency at Hurley Children's Hospital, where more than 2,000 children have been tested. She is credited with bringing the problem to the public's attention after state agencies initially dismissed her concerns.
"It was frustrating that it went on for so long," Hanna-Attisha said, complaining that even since the state began taking action, "everything has been slow."
"The state was telling everybody, 'It's fine, relax. ... It's safe,"' even as people complained that the water looked cloudy and tasted bad, said community activist Melissa Mays. "They lied."
Mays, her husband and three sons ages 11, 12 and 17 are taking medication to reduce high lead and other heavy metal levels in their blood.
"Like everybody else, we drank and cooked with it because they told us it was safe," she said.
Rabecka Cordell said she learned from her doctor that both she and her 5-year-old son, Dayne, have lead poisoning. She said she also has leukemia, and her son has learning and speech disabilities.
She won't even bathe in the water and won't wash her son in it.
"It's ridiculous," Cordell said.
Hurley Children's Hospital is distributing 10,000 booklets on mitigating the effects of lead on children, including recipes high in iron, calcium and vitamin C. Adding to the challenge is that there are few grocers with fresh produce within Flint city limits. At a local farmers market, the hospital offers weekly recipe and cooking demonstrations with lead in mind. The first one was hearty egg burritos.
Nutrition "has a huge mitigating role," Hanna-Attisha said.
She urged parents to consult early and often with a pediatrician.
In consultations, the doctor said, "we need to give families hope that with secondary prevention interventions, not every kid is going to have problems."
Joining calls from outraged Flint residents, Democratic presidential candidate Bernie Sanders on Saturday called for Snyder to resign.
"There are no excuses. The governor long ago knew about the lead in Flint's water. He did nothing. As a result, hundreds of children were poisoned. Thousands may have been exposed to potential brain damage from lead. Gov. Snyder should resign," Sanders said in a statement.
"Because of the conduct by Gov. Snyder's administration and his refusal to take responsibility, families will suffer from lead poisoning for the rest of their lives. Children in Flint will be plagued with brain damage and other health problems. The people of Flint deserve more than an apology," Sanders said.
Members of Michigan's congressional delegation applauded the FEMA declaration. Democratic U.S. Sen. Debbie Stabenow said she will push for long-term resources, and Democratic Rep. Dan Kildee said residents "deserve every resource available to make sure they have safe water and are able to recover from this terrible man-made disaster created by the state."
The U.S. Justice Department is helping the Environmental Protection Agency investigate the matter, and state Attorney General Bill Schuette has opened his own probe, which could focus on whether environmental laws were broken or if there was official misconduct.