Ashburton District Mayor Angus McKay said he felt "weak at the knees" when he heard about the shooting at the town's Work and Income office.
"Ashburton is not this kind of town," he said.
Social Development Minister Paula Bennett called it "an extreme situation and tragedy", adding that all resources were going into looking after WINZ staff.
She was travelling down to the town this afternoon.
Public Service Association (PSA) said the shooting was a tragedy and nobody should go to work in fear that they might not return home.
PSA National Secretary Richard Wagstaff said "Our thoughts are with all those affected by this tragedy,"
"We don't know what the cause is, but we will be supporting our members from Ashburton Work and Income at this terrible time.
"That two people have died and one more is in a serious condition is inexcusable, and we hope the Police can bring the shooter to justice.
"Nobody should go to work in the morning without returning home that same day.
"Our 6500 members working at Ministry of Social Development will have their Ashburton colleagues in their thoughts," Wagstaff said.
"We have no information at this stage about whether any of our members are among the victims," Wagstaff said.