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Shots were fired through the office's front window last Thursday night, Mr Harawira told Radio New Zealand.
He said he was taking the threat seriously.
"It is a worry, I get criticisms, I get threats - I even get death threats - but when people start taking shots at your office it's a whole different ball game.
"It takes it to a completely different level and it worries me about my staff and about the whanau who come to that office to get help."
The office was surrounded by houses and was near a childcare centre, he said.
"It's very scary."
Staff sometimes work late into the evening, Mr Harawira said.
Police were investigating, but had not yet spoken with the MP.
"We haven't had any specific advise, I understand, as to what steps we should be taking - moving out or putting in bullet-proof glass or anything like that."
He was considering getting Parliamentary security to install stronger glass on the front windows.
Over the past five years Mr Harawira had received numerous threats and he had contacted police about the serious ones.
"The sad thing is you kind of get used to it, but when people start taking shots at your office, then you worry."
He had no idea who was behind the latest threat.