Two field hospitals set up to accommodate the anticipated overflow of COVID-19 patients in Massachusetts have struggled with staffing shortages as the pandemic's second surge ramps up, officials told GBH News.

Staffing was the “biggest concern” before launch at a field hospital in Worcester’s DCU Center, according to that site’s medical director, John Broach.

Within its first three weeks of opening, the Worcester field hospital has taken in 172 patients — nine more than the 163 patients admitted during the spring surge.

The Worcester facility has 80 staff members and can accommodate up to 60 patients at once. The facility could increase its capacity to 220 patients if staffing is available, according to Broach. Frontline workers at the Worcester field hospital have been vaccinated at least once.

“I think we expected that the second surge would be worse,” Broach told GBH News on Tuesday. “With the dual mission of continuing to provide really good COVID-19 care while also allowing the brick and mortar hospitals to continue more of their regular care, I think we did expect to see a higher volume this time around.”

Another alternative care site operated by Lowell General Hospital is opening on Monday, a week after the site’s initial planned launch. The field hospital, located at Umass Lowell, can now accommodate 14 beds, with an eventual total capacity of 77 beds, according to hospital spokesman Will Courtney.

“We had initially planned to do a soft launch of the site this week to strictly Lowell General Hospital patients,” Courtney told GBH News on Tuesday, “but did not wind up doing so due to the need to secure additional staffing for the site.”

In Worcester, the last four days have seen an increase in admissions, representing a broad and gradual rise, with more new patients arriving and fewer patients being discharged, according to Broach.

“On average, we discharge 5-10 patients per day and get, you know, between five and 10 admissions a day,” Broach said. “The last few days, it's been heavier on the admissions than the discharges.”

Though holidays contribute to a higher number of COVID-19 cases, Broach says the increase isn’t necessarily attributable to a post-holiday surge.

“I think the overall caseload is just increasing, and we expected to see that the second surge was going to be worse than the spring,” Broach said. “Respiratory viruses tend to be worse in this time of year, and certainly pandemics that have two waves tend to be worse the second time.”