RNZ communications manager John Barr said staff in the Wellington newsroom were subdued following the attack, which happened in broad daylight in a public place.
"We take seriously the safety and security of all of our staff, particularly those who are working overnight shifts,'' he said.
The man was wearing was wearing a grey, long-sleeved, striped shirt, faded blue jeans, a grey cotton jacket and carrying a black adidas backpack, Mr Miller said.
Police wanted to hear from anyone who saw the incident or was in the area between 5.30am and 6.15am.
The incident is the second tragedy to hit RNZ in as many months - last month, production secretary Carol Louise Davidson, 63, and her new husband, Christopher Mark Bishop, 58, were killed when they lost control of their motorbike while on honeymoon in Nepal.