This March 23, 2011 photo shows the El Dorado Correctional Facility near El Dorado, Kan.

Topeka ? An unspecified number of inmates refused to return to their cells for at least several hours Thursday at Kansas’ second-largest prison, and legislators said they’re concerned that short staffing and an increasing prisoner population led to the problem.

The state Department of Corrections reported that all inmates had returned to their cells at the maximum-security prison in southern Kansas by Thursday evening. Spokesman Todd Fertig said no staff or inmates at the El Dorado Correctional Facility were injured and that the incident was resolved “without any use of force.”

The department’s report that the incident had been resolved came shortly after a leader of a union representing corrections workers said the situation was “not under control.” Robert Choromanski, executive director of the Kansas Organization of State Employees, said corrections officers reported that the prison was locked down and inmates took control of the gym and other areas of the facility.

The union has said for weeks that the prison is understaffed, and its inmate population has increased by about 200 inmates over the past three months, to about 1,900. The state has boosted its capacity by double-bunking some cells as it transferred inmates in, including from other prisons.

“The pressure of having fewer staff, more inmates and double-bunking was a recipe for some type of occurrence like this,” said state Rep. J.R. Claeys, the Republican chairman of a budget subcommittee on public safety.

Fertig said he didn’t know the number of inmates involved in Thursday’s incident or how it started. He confirmed reports from the union that officers from other prisons were called in to deal with the incident but said that’s normal procedure.

He said inmates never had access to weapons and that the department “responded by ensuring the security of the facility and methodically returning the offenders to their cell houses.”

The El Dorado Correctional Facility houses some of Kansas’ most dangerous offenders, despite having a mix of medium- and maximum-security cells. The prison opened in 1991 about 30 miles (48 kilometers) east of Wichita.

The Department of Corrections lists the prison’s capacity as 1,955 inmates, but the official figure was about 1,500 inmates three months ago.

Choromanski noted the prison has dozens of unfilled staff vacancies and officers must work overtime.

Last week, the Department of Corrections confirmed that the prison was putting 12-hour shifts into effect for at least 90 days as it attempted to recruit more workers. Warden James Heimgartner called the change a “temporary staffing pattern” in a letter to employees.

Kansas’ prisons struggle to fill vacancies because the pay for correctional officers is lower than the pay at federal prisons and even some county jails.

At the same time, moving prisoners and double-bunking cells at the El Dorado prison “creates a very dangerous situation” for inmates and staff, said state Sen. Laura Kelly, of Topeka, the ranking Democrat on the Senate budget committee.

“And ultimately it could put the general public at risk should these lockdowns, sit-ins escalate from there and folks escape,” Kelly said.

But Fertig said all critical security posts at the El Dorado prison are “appropriately staffed.”

— Associated Press writers Roxana Hegeman in Wichita, and Margaret Stafford and Heather Hollingsworth, in Kansas City, Mo., contributed to this report.