DETROIT -- The state of Michigan can't meet all the needs of Flint residents whose water system has been contaminated by lead, Gov. Rick Snyder said in a request for a federal disaster declaration and millions of dollars that could pay for clean water, filters and other essentials.

Snyder's letter to President Barack Obama paints 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 result of using the Flint River as the city's drinking water for 18 months.

"Mistrust in government is at a heightened level," Snyder, a Republican, said in a request dated Thursday and released to The Associated Press.

The application seeks help from all available federal programs. Snyder said 90 days of clean drinking water could cost $10.3 million, and home filters, filter cartridges and testing kits could cost $31 million over a year.

"The governor has made a request through the formal process, and that's a request that we'll consider expeditiously," White House spokesman Josh Earnest said Friday.

The tap water in Flint, population 99,000, became contaminated after the city in 2014 switched its water supply 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. Exposure to lead can cause behaviour problems and learning disabilities in children as well as kidney ailments in adults.

The National Guard is distributing free water, filters and other supplies.

Over the long term, replacing old lead service lines at Flint homes and other private properties could cost $54 million, the governor told the president.

That is a huge expense for a city where nearly 60 per cent of residents get food stamps and median household income is 50 per cent less than the statewide figure, Snyder's letter said.

"The state has responded, but the response needs far exceed the state's capability," he said of Flint's water problem.

Michigan's request seems unusual, if the form used by the Federal Emergency Management Agency is any indication. There are boxes for 18 different disasters but none for "public health" as listed by the Snyder administration. FEMA didn't immediately return a message seeking comment.

"Replacing infrastructure and keeping a community supplied with safe drinking water for an extended period of time is expensive. The costs add up quickly and the state simply can't absorb them all," said Snyder spokeswoman Meegan Holland.

Separately, at least 10 people have died from Legionnaires' disease in Genesee County, due to the Legionella bacteria, although state and local health officials say they can't make a definitive connection to the water.

"We're finally getting the attention that we need and deserve," Flint Mayor Karen Weaver said in response to Snyder's request for federal disaster aid.

A state task force recently faulted Snyder's Department of Environmental Quality for not requiring Flint to treat the river water for corrosion and for its derisive response to the public's fears. The head of the department and his spokesman resigned.

State Attorney General Bill Schuette said Friday that his office was investigating if any laws were broken. He declined to elaborate on the scope of the probe. The U.S. Justice Department is also investigating.