Live video showed shaking students being evacuated with their hands in the air so officers could be sure they were not armed.
Officers with rifles rushed across the field to check the students for either injuries or weapons before taking them to a local church, where parents were gathered waiting for news.
KIRO-TV reported that the school was placed on lockdown at 10.45am Pacific time after students and teachers called 911 about multiple shots fired in the cafeteria.
As of 16.30pm Easter time, a male victim being treated at Harborview Medical Center emerged from surgery but was still in a serious condition.
A student who spoke to CNN on the phone from inside the school described a grisly scene inside the cafeteria, telling the news outlet: ‘There was blood everywhere.’