Three men and two women managed to sneak into the hearings on Tuesday despite efforts by the federal review panel to limit access, said Vancouver Police Sgt. Randy Fincham.
Police believe a visitor who was there with someone scheduled to speak at the hearing allowed the protesters access to the hearing room around 11 a.m.
"The demonstrators when they entered the hearing, they began moving through the hearing room, blowing whistles and causing a ruckus and interfering with the hearing that was taking place," Fincham said in an interview.
"The members of the joint review panel that were conducting the hearing asked the five demonstrators to leave the building, as it is a private hearing.
"The five demonstrators refused to leave and they were subsequently arrested by the police ... for assault by trespass."
Three men and two women were expected to be released Tuesday afternoon, if they met conditions for release, Fincham said.
Police have an enhanced presence at the hearing site, he said, and will continue to maintain a presence until eight days of scheduled hearings are complete.
One woman was arrested on Monday night, after she managed to evade security and get into the lobby of the hotel during a mass demonstration marking the first day of hearings in Vancouver.
The nationwide Idle No More movement merged with ongoing protests against oil pipeline projects proposed for British Columbia, to bring about a thousand people out for rally in the city's Victory Square on Monday night. Police say about half of them marched to the hearing site.
Fincham said one group of protesters was aggressively taunting police and tried to gain access to the hotel, but only the one woman managed to get into the lobby.
"She was arrested and taken to jail," Fincham said, adding that she was released later that night.
Protest organizer Maryam Adrangi said the demonstrators arrested Tuesday don't support the hearing process.
They went into the hearing room to reveal T-shirts emblazoned with anti-pipeline slogans, and they taped off the room as a "climate crime scene."
In particular, pipeline opponents are angry that the review panel is not hearing evidence about emissions from the Alberta oil sands and the greater issue of global warming.
"They are following how this is becoming increasingly less democratic and they went in there to expose that they aren't going to let unjust legislation stop them from having their voices heard," Adrangi said.
She cited petitions, protests and several municipal motions — including one from Vancouver — that oppose both the Northern Gateway project and a plan by Kinder Morgan to more than double the capacity of its existing TransMountain pipeline from Alberta to Vancouver.
"There have been endless ways that people have said no, so if the public was genuinely being heard then this project would have already been scrapped," Adrangi said.
A company spokesman said the hearing interruption was "disappointing."
"These proceedings are intended to give voice to British Columbians and some individuals saw fit to interrupt that process," Enbridge spokesman Todd Nogier told reporters outside the hearing room.
If approved, the almost 1200-kilometre-long twin pipeline would carry about 525,000 barrels of petroleum per day from Alberta to the B.C. coast for shipment by tankers.
Community hearings were held previously in Victoria, and a one-day hearing is scheduled in Kelowna later this month.
The panel is limiting access to the hearings room to participants. Members of the public are able to listen to submissions in another location. The hearings are also being streamed live on the panel website.