Mayor Michael B. Hancock issued an emergency declaration Thursday because of the recent wave of immigrants fleeing Central and South America to Denver – which has to date a price tag for taxpayers of about $800,000.

Staffing is one of the main drivers of the cost, Hancock said at a press conference. Other expenses include food, clothing, cost, security and transportation.

The mayor’s press conference marked the city’s second briefing in a week on the unfolding immigrant situation.

The city opened its first emergency shelter in a recreation center on Dec. 6 and second one Wednesday. Since last week, more than 400 immigrants have arrived to the Mile High City, mostly from El Paso, Hancock said.

“When we started seeing this influx last week, when residents started sending us messages, they weren’t asking, ‘Why are these people here and why aren’t we stopping them?'” Hancock said. “They were asking, “How can we help?'”

Hancock added, “That’s the hallmark of a welcoming city. And I’ve never been prouder of our city.”

Since Monday, 247 immigrants have come to Denver, Hancock said. The city and its partners – shelters, churches and nonprofit groups – are housing 411 migrants.

“So, let me be frank, this influx of migrants, the unanticipated nature of their arrival and our current space and staffing challenges have put an immense strain on city resources,” Hancock said.

The city has not been tracking the flow of immigrants and it’s unclear whether this reflects a year-over-year increase.

Without additional resources, Hancock said he feared a humanitarian crisis could unfold here.

The emergency declaration, Hancock said, will allow the city to expedite its procurement process, among other things.

While city officials had anticipated the arrival of some immigrants, the sheer volume caught the city flatfooted.

Roughly 90 immigrants arrived last Monday, triggering the city’s response.

The majority of U.S. immigrants reside in the country legally.

An estimated 190,000 were living in Colorado in 2016, according to the most recent study by the Pew Research Center, which conducts research on a wide range of topics.

To put that number into perspective, California has the most populous undocumented immigrant population with 2.2 million migrants, while Maine, Montana, West Virginia and Vermont have the least with fewer than 5,000.

This inpouring of immigrants illustrates the U.S. border crisis spilling over into other cities, including Denver, which is more than 600 miles from the Mexican border in El Paso, Texas.

“We’ve gotta fix this immigration issue,” Hancock said.

Hancock added, “This is going to continue to happen, continue to overwhelm cities all over the country until Congress works on fixing the situation.”