School children and grandmothers were among the 150 or so protesters outside the New Zealand Petroleum Conference in New Plymouth.
The protesters originally said they were planning a peaceful demonstration but events started getting physical when delegates tried to enter the TSB Showplace for the start of the two-day event.
Protesters jumped over the barriers and linked arms directly outside the entrance, physically blocking the doorways as delegates arrived.
Protesters were also present at the back entrance to the venue and police forcibly removed some protesters from both entrances.
The Petroleum Exploration and Production Association of New Zealand (PEPANZ) chief executive Cameron Madgwick said the annual conference has always attracted protests and event organisers worked closely with the New Plymouth District Council and the police in the lead up to the event.
"While the protest action was expected, it is still disappointing. We want to use the conference to celebrate Taranaki's oil and gas industry and the incredible contribution it has made to the region, rather than it being targeted by protestors to cause disruption to the community."
Particularly disappointing this morning, said Mr Madgwick, was the delay to the morning powhiri.
"We had a children's kapa haka group coming in from Stratford and the protesters outside meant their arrival was delayed, as was the arrival of the kai karanga from Ngati Te Whiti.
"This is pretty disrespectful to the tangata whenua really."
Despite the protests, the conference was well underway, said Mr Madgwick.
"We're completely caught up and have already had some fantastic speakers. Everyone is really enjoying it and getting great stuff out of it."
The kapa haka kids were kept away from the protests but six-year-old Keri-Lee White was one of the youngsters actively particpating.
"I'm here for the water, we want clean water so we can swim in it," she said.
The youngster blew bubbles as other protesters sang and cheered loudly as a group of protesters successfully stopped some delegates from entering the building.
"We don't want them here, they are trying to make our water dirty," the Waitara schoolgirl said, adding she had taken the day off school to attend the protest.
Another youngster, Frances Edwards, 8, had also taken time off from school in Auckland to attend the protest.
"I am here for the whales and dolphins because they can't speak."
Grandmothers Jill Whitmore and Ineke de Raad had both travelled some distance to participate in today's protest.
From Auckland and Tauranga respectively, the two 71-year-olds said they were protesting because they were worried for their grandchildren and future generations.
"We have the technology and science now to do move away from fossil fuels, it is time to get cracking and do it," said Whitmore.
de Raad said retirement had afforded her the opportunity to "get out and start making a difference".
Mike Smith, a protester from the Far North, interrupted protesters singing to announce some breaking news.
"The Patea Maori Club were booked to perform at this event tomorrow," he told the crowd, and booing changed to cheers as he continued "and now they have found out what the event was, they are refusing to come.
"They will not support this event".
Smith said he received the news in a text message from Ngati Ruanui CEO Debbie Ngarewa-Packer.
"She just texted me, it's great news."
With the conference set out over two days, protests were expected to continue throughout and a police presence was being maintained at the venue.
"I'll be here until the last delegate goes home, if we don't speak now, we won't have a world to live in later," said Tai Willoughby, who had travelled from Auckland to protest.
"I hitch-hiked down and will sleep on the street tonight if I have to, I won't be quiet and I won't stop talking about this."