OAKLAND, Calif. -- Police were investigating the death of an East Bay patient Saturday morning that hospital officials say was fatally dosed with an unknown medication by a replacement nurse brought in from out-of-state during a recent nurse strike.

Alta Bates Summit Medical Center in Oakland is where police were called early Saturday morning to investigate the death of a 66-year-old woman.

The woman was a cancer patient who had been receiving treatment at Alta Bates since July.

Oakland Police said that on Saturday morning, one of the nurses here made a fatal medical error and were told "a patient had died after being administered a non-prescribed dosage of a medication that is known to be lethal in the manner in which it was administered."

Police wouldn't say what type of medication or how much was given Sunday morning.

The nurse who gave the medication was a replacement brought in by the hospital from another state after regular nursing staff at Alta Bates and nurses at more than 30 other California hospitals went on strike on Thursday.

In response to the strike, Alta Bates and a few other hospitals locked out participating nurses for five days.

About a half dozen security guards stood outside the hospital Sunday morning as the lockout continued, despite the patient’s death.

The California Nurses Association issued a statement Sunday claiming that Summit Hospital administrators had barred regularly employed nurses from returning to work Friday after a one-day strike by 23,000 nurses at Sutter, Kaiser Permanente and Children's hospitals on Thursday.

"We are calling on the Department of Public Health to carefully examine conditions in Sutter hospitals that have locked out RNs," CNA legislative director Bonnie Castillo said in a statement.

A group of nurses plans to hold a candlelight vigil at Alta Bates Summit Medical Center Sunday night at 7 p.m. The hospital was located at 350 Hawthorne St.

Police began conducting an investigation into the patient’s death Saturday. Officers told KTVU that the nurse at the center of the incident was questioned by detectives the same day.

The Alameda County District Attorney's office announced Saturday that it planned to review the case and the Oakland Tribune reported Sunday morning that the hospital said it was conducting its own investigation into what went wrong.