Ms Hawira organised the protest to give people in Whanganui the opportunity to let their opinion on seabed mining be known.
The Castlecliff protest follows several others in Patea over the Environmental Protection Agency's decision last month to allow Trans Tasman Resources to mine ironsands off the south Taranaki coast.
Whanganui District councillor Jenny Duncan went to the protest because she was "horrified" by the EPA's decision.