A student singled out by Oregon college gunman Christopher Harper-Mercer as the "lucky one" to survive and deliver a package to police has spoken for the first time about the massacre.

In a written statement, Mathew Downing, 18, said his ears were already ringing from previous shots fired when Harper-Mercer entered the Umpqua Community College classroom on October 1 and he thought what was happening "couldn't be real".

Mr Downing said Harper-Mercer had two handguns that he reloaded during the incident and that at one point was "firing on people who were just lying there".

One student picked up a desk to defend herself but Harper-Mercer fired at her anyway, hitting her in the leg, he said.

Mr Downing said that after Harper-Mercer was hit by police gunfire, he lay down and shot himself in the head.