Unaccompanied minors are crossing the U.S. Southwest border in growing numbers again, sparking concerns that the new influx of children could eventually approach the levels that last year prompted the Obama administration to declare a humanitarian crisis.

In October and November, more than 10,500 children crossed the U.S.-Mexico border by themselves, the vast majority from El Salvador, Guatemala and Honduras, according to U.S. government data analyzed by the Migration Policy Institute, a nonpartisan think tank. That’s a 106 percent increase over the same period last year, reflecting a steady increase that began in March.

The numbers are still far below the peak period last year, when more than 10,600 unaccompanied minors crossed the border just in the month of June, swamping federal resources. And the administration, widely believed to have missed the warning signs before the previous surge, “is certainly a lot more concerned and on top of it than they were two years ago,” said Marc Rosenblum, deputy director of the U.S. immigration policy program at the policy institute.

Still, the administration and immigrant advocates are growing increasingly worried, especially because some of the same conditions that drove last year’s surge, including gang and drug-related violence in Central America, have grown even worse. The Department of Health and Human Services, which is required to shelter and care for the children after they are apprehended by the Department of Homeland Security, last week opened a new, 700-bed shelter in Texas and is planning to open another 300-bed facility in Texas as early as Friday. A third, 400-bed facility in California may also be needed, officials said.

“This sharp increase in children entering this country is a result of many factors,” HHS Secretary Sylvia Burwell wrote in a letter last week to the House appropriations committee. “While it is impossible to know if these trends will continue for the duration of the fiscal year, we are very concerned about having adequate resources to meet the needs of the unaccompanied children.” The letter urged lawmakers, who are negotiating final details of a year-end spending deal, to grant President Obama’s request for a contingency fund of up to $400 million if the numbers of children continue to grow, beyond the nearly $950 million already requested for the unaccompanied minors program.

The concern also extends to the state level, where Texas Gov. Greg Abbott (R) on Tuesday ordered Texas National Guard troops to remain at the Mexico border, extending a mission that began last year at the height of the surge. It is unclear how many troops will remain.

In a joint statement, HHS and DHS said the entire administration “has been closely monitoring these current trends and coordinating across the whole of government to ensure an effective response to any changes in migration flows.” The statement added, “We continue to aggressively work to secure our borders, address underlying causes and deter future increases in unauthorized migration, while ensuring that those with legitimate humanitarian claims are afforded the opportunity to seek protection.”

A DHS official, speaking on condition of anonymity because the official was not an authorized spokesman, added that the government “is definitely concerned, but it’s really, really hard to predict what’s going to happen.”