He said protesters arrived at the gates at 7am.
"We have started at the gates around the main offices and the [mining] activity shut down and then we kind of extended to a few extra gates around the site. We are currently occupying four different gates and we greatly impacted operations of the mine today."
He said there were just over 30 activists at the protest, which is expected to last all day.
Hornet said police had turned up but were not communicating with them directly.
The coalition wanted to send a signal that companies like Bathurst did not have the public's best interests at heart, he said.
"They are only acting in their own agenda and with their own profit in mind, while they are actually jeopardising our future when they do that."
He said the goal was to permanently shut down all mining in New Zealand.
"We want [Bathurst] to recognise that and start a conversation and not pretend business as usual can continue."
Bathurst Resources Limited chief executive Richard Tacon said the company was concerned for the safety of "the trespassers".
"We closed down site activities this morning to reduce risk to the trespassers and to our workforce.
''We appreciate the assistance of the New Zealand Police in ensuring the ongoing safety of all concerned. The site is expected to return to normal lawful activities this afternoon."
Police said some protesters had been arrested after they chained themselves to an internal gate within the mine, blocking access.
They have been removed from the area.
In a statement, police said: "While police recognise the lawful right to protest, our priority is to ensure safety and uphold the law. In this instance it has not been safe for the protesters to be in this area.
"Police will remain at the site and will continue to respond appropriately to any issues that may arise."
- RNZ
