(NewsNation) — Denver recently declared a state of emergency following the unexpected arrival of hundreds of undocumented migrants.

Unlike other cities that have been impacted by the busing of migrants directed by governors in border states, Denver’s surge appears to be driven by coordination between asylum seekers and nonprofit organizations. The city has seen over 900 undocumented migrants arrive since early this month.

Denver Mayor Michael Hancock told “NewsNation Prime” that the city’s resources are being strained by the arrivals.

“We’re going to run out of capacity to serve them,” he warned. “And the reality is … as they come, we’re going to run out of these finite resources. And, unfortunately, we’re going to have some folks who are wandering around Denver on very cold nights.”

Hancock said that both space and staffing are issues when it comes to serving the migrants.

“It’s a very challenging time for us,” he said. “Our resources are stressed. But the biggest issues for us (is) shelter space and volunteers or staffing for the shelters.”

Hancock called on the federal government to pursue a solution for immigration.

“It is very important, urgent, that Congress work with (President Joe Biden) to come up with a strategy around immigration. Cities are once again bearing the brunt and having to respond because of the inactivity of Congress,” he said.