It is too early to say when a water treatment plant in Mississippi's state capital of Jackson that failed last week leaving tens of thousands of people without clean tap water can be fixed, the head of the U.S. Federal Emergency Management Agency (FEMA) said on Sunday.

Deanne Criswell told CNN's State of the Union that FEMA's current focus was on ensuring a supply of bottled drinking water while working with federal partners to see what needed to be done to bring the plant back to full operational capacity.

"I think it's still too early to tell," said Criswell, whose agency has been charged by President Joe Biden's administration with coordinating disaster relief efforts for Mississippi, when asked when the plant might be fully operational again.

"It's going to happen in phases," she said after visiting Jackson on Friday. "The focus right now is making sure we can get bottled water out, but also we are providing temporary measures to help increase the water pressure, so that people can at least flush their toilets and use their faucets.

"The longer-term and mid-term about how long it's going to take to actually make it safe to drink, I think we have a lot more to learn about what it's going to take to get that plant up and running."

Complications from recent floodwaters knocked Jackson's O.B. Curtis Water Plant offline on Monday night, leaving most of the state capital without safe running water and highlighting the problem of America's crumbling infrastructure, which Biden's administration has vowed to address.

Mississippi Governor Tate Reeves declared a state of emergency for Jackson and surrounding communities last week, warning the area's 180,000 people to avoid drinking tap water.

Mississippi activated its National Guard on Tuesday to help distribute water and Biden's administration approved an emergency declaration last week and ordered federal assistance to supplement the state's response.

The crisis has hobbled Jackson, forcing many stores and restaurants shut, while the public school system and Jackson State University had to move classes online.

Jackson Mayor Chokwe Antar Lumumba told ABC News the city's water infrastructure was broken due to wear and tear and due to climate change.

He said the city may have water that is approved as fit for drinking within days rather than weeks, but ensuring a "reliable, sustainable" water treatment facility was "a much longer road ahead."