The store was closed for business Wednesday afternoon as employees inside cleaned up the bloody scene.
Police say a customer picked up several saws and began cutting into both of his own arms.
"The witnesses said they first noticed him in the action of cutting himself with the saws," said West Covina Police Corporal Rudy Lopez. "The scene itself was quite gruesome."
As 911 was called, an off-duty paramedic happened to be in the same aisle and rushed to help.
"The paramedic suggested that we get some twine and some rags from within the store, at which time when they acquired that, both the officer and the paramedic applied tourniquets to both arms, probably saving his life," said Lopez.
The man was hospitalized in unknown condition. He was not immediately identified. He was in surgery at Queen of the Valley Hospital.