WASHINGTON (DC News Now) — Mayor Murial Bowser requested the National Guard’s assistance in a “humanitarian crisis,” as the city has seen a surge in migrants bussed from Texas and Arkansas.

According to a letter obtained by DC News Now’s partner NewsNation, Bowser requested the D.C. National Guard’s help on July 19 “to prevent a prolonged humanitarian crisis” in the District.

In a letter signed by Christopher Rodriguez, D.C.’s director of the Homeland Security and Emergency Management Agency, it was noted that more than 4,000 migrants on nearly 200 buses have come to the nation’s capital in the past four months.

“…the pace of arriving buses and the volume of arrivals have reached tipping points,” the letter addressed to the Office of the Secretary of Defense reads. “Our collective response and service efforts have now become overwhelmed: the regional welcome center we helped establish in Montgomery County, Maryland is at capacity; our homeless services system is already under great strain; and tragically, many families arrive in Washington, DC with nowhere to go…”

On Thursday, Bowser answered questions about the situation at an event that was unrelated to the influx of people.

“We are very focused and we continue to be very focused on having the federal government do its part and take the lead in addressing what we see as a growing humanitarian crisis,” Bowser said.

She noted that recently, the federal government has intervened with refugees from Afghanistan and Ukraine.

“We need to make sure that there is a national response, not an ad hoc city-by-city, state-by-state response,” she said. “We know that the federal government does this because we see this type of response with Afghan refugees. And now we see it with people who are coming to the United States from Ukraine. So there is a robust federal response that helps people with transportation onto their final destinations, and even givingthem a legal route to work.”