The National MP was holding a media stand up outside the Copthorne Hotel when the woman threw the phallic object, shouting "that's for raping our sovereignty."
She was taken away by police.
Steven Joyce talks to Duncan Garner about the incident:
Prior to the incident, pouring rain and the absence of Prime Minister John Key had turned what had been billed as one of the most tense showdowns at Te Tii Marae in years into a bit of a fizzer.
February 5 is the day politicians of all stripes descend on Waitangi's lower marae and in previous years it's been the scene of fraught face-offs, scuffles and mud-slinging.
Planned protests against the just-signed Trans-Pacific Partnership trade deal didn't eventuate, with only about 100 activists - many carrying flags and banners - welcomed on to the marae this morning.
Mr Key's decision not to go to Waitangi at all, amid concerns he'd be subject to a "gagging order" stopping him from speaking freely in the whare, is likely to have taken much of the heat out of what had the potential to be a hostile situation.
But he denies he's running scared.
"I've been very keen to go, I gave a commitment that I'd go every year," Mr Key told reporters.
In 2007, when he was opposition leader, Mr Key promised he would go to Waitangi every year.
But because he hasn't been able to get assurances he'll have full speaking rights on the marae, as he has in previous years, Mr Key has made the call not to go this time.
A number of government ministers are up at Waitangi, but none made the pilgrimage to Te Tii Marae. They are expected to be attending other events, including the iwi leaders forum and possibly the Waitangi Day dawn service at the upper marae.
Green Party co-leaders Metiria Turei and James Shaw, along with a contingent of their MPs, were welcomed on to Te Tii Marae without incident.
But the Labour Party, including leader Andrew Little, were forced to wait in the rain at the gates for about an hour before their powhiri.