Allina Health, one of Minnesota’s largest clinic and hospital systems, suffered a computer network failure on Wednesday night, but officials said medical care was not affected and there is no evidence that it was caused by a malicious hack or external tampering.

“We have no evidence that this was the result of anything coming from outside our systems,” Allina said in a written statement provided by spokesman David Kanihan. He said the organization is still trying to pinpoint the cause.

Patient care was maintained, the statement said, because the hospital has backup, or “downtime,” computers and procedures that allow doctors, nurses and other caregivers to see up-to-date patient records.

Prescription drug dispensing machines are linked to the network, but were switched to manual modes so that caregivers could get timely medications for patients.

“In this situation, the procedures worked well,” Kanihan said, noting that the timing was lucky because the outage occurred during the evening, when patients are sleeping and no surgeries are scheduled.

The network was restored around 2 a.m.

The outage affected the entire Allina system, which consists of 65 clinics and 22 hospitals, including Abbott Northwestern in Minneapolis, United Hospital in St. Paul and Mercy Hospital in Coon Rapids and Fridley.

Network outages have been reported periodically by U.S. hospitals and health care systems. Hospital Corporation of America reported an outage that lasted a day in 2015 and affected numerous hospitals in Florida and other states.

Boulder Community Hospital in Colorado endured an outage in 2013 that lasted 10 days.