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Washington: US President Donald Trump has approved an emergency declaration for the District of Columbia, permitting federal agencies to provide disaster assistance to tackle a massive sewage spill in the Potomac River.

The spill began in mid-January, when part of a major DC Water sewage pipeline called the Potomac Interceptor collapsed, flooding the Potomac River with about 886 megalitres of wastewater. The sewer line carries about 227 megalitres of wastewater daily from the Virginia and Maryland suburbs to DC for treatment. The cause of the spill remains under investigation.

The US Environmental Protection Agency will lead the federal response to the spill, according to a news release from the agency. The EPA is co-ordinating with DC Water to ensure measures are taken “to protect public health and prevent additional overflows until the pipe is repaired and the Potomac Interceptor is fully functional again”. Repairs are due to be completed by mid-March, before events in the region celebrating the 250th anniversary of the US are set to begin.

The Federal Emergency Management Agency will also be “deploying a team to support incident management” and “working directly with local officials and federal partners to co-ordinate federal resources”, a social media post from Homeland Security Secretary Kristi Noem said.

FEMA said the assistance would be directed to DC and the area where the district has responsibilities in Maryland and Virginia.

Washington Mayor Muriel Bowser declared a public emergency on Wednesday (Washington time) and requested federal help with the clean-up. She also requested a presidential disaster declaration and asked the federal government to reimburse the DC government and DC Water for costs associated with the spill and recovery effort.

DC Water chief executive David Gadis estimated the repair and remediation would cost $US20 million ($28 million).

Trump, who previously criticised Bowser and other Democratic elected officials in the region over mishandling the spill, signalled on Thursday that the federal government would help with the recovery.