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Michigan has deployed the National Guard to distribute bottled water and filters to residents in Flint who are struggling with a water crisis.

The move ordered by Governor Rick Snyder comes after recent tests found elevated blood-lead levels in children living in the city.

Old plumbing leaked lead into homes after the city switched water sources.

More than 30 Guardsmen will be in place by Friday in Flint, which has 99,000 people.

Mr Snyder has described the situation as a "crisis" and declared an emergency last week.

The city switched its water source from the city of Detroit to the Flint River in 2014, in order to save money.

The water from the river leached lead off old plumbing, which then made its way into people's homes.

They have since switched back to Detroit's water.

In October, testing revealed increased lead levels in water supplies and in children's blood. Lead exposure can cause learning disabilities and behavioural problems in children.

According to the Mayo Clinic, young children are especially vulnerable, and exposure "can severely affect mental and physical development".

The clinic says that at high levels, lead poisoning can cause death.

Image copyright AP

A task force set up by the governor and the state auditor general have blamed the state's Department of Environmental Quality for not mandating that the city treat the water for corrosive elements and for downplaying residents' concerns.

The director of that agency resigned last month.

On Monday, the governor issued a directive that created a committee to work on long-term solutions for resolving the crisis and addressing health concerns.

On Tuesday, braving cold temperatures and 3ins (7.62cm) of snow, eight teams of volunteers fanned out across the city under the escort of state troopers and sheriff's deputies to deliver bottled water, filters and lead test kits.

The New York Times has reported that the National Guardsmen could hit the streets as early as Wednesday.

The paper said that the troops would take over distribution sites currently being manned by American Red Cross volunteers, allowing the volunteers to begin door-to-door operations.