John Key says his decision to boycott Te Tii Marae this Waitangi Day was about his and his staff's safety.

The prime minister said he refused to attend the events because his safety couldn't be guaranteed following Thursday's singing of the Trans-Pacific Partnership.

Mr Key said the throwing of sex toy at economic development minister Steven Joyce was appalling.

He said protests could have turned violent if he had turned up, and taking that risk wouldn't be fair for the people around him.

However he said if protests did turn violent, it wouldn have harmed New Zealand's international reputation.