Police had not released the names of the deceased people at edition time.
"One moment of inattention appears to have caused this," Mr Symonds said.
"It reminds people to make sure they drive safely and get to their destination.
"It doesn't matter how late you are when you get there, just get there safely and spend time with your family and loved ones. We don't want this to happen."
Dozens of emergency services workers and volunteers were at the crash scene and just before 4pm a fleet of hearses arrived after a kaumatua had blessed the site.
Northland road policing boss Inspector Murray Hodson said the police Serious Crash Unit was investigating.
Mr Hodson said police were unable to ascertain the victims' identities at this point, but he could confirm they were of Asian descent.
"Police are currently working with emergency services to try and carry out the investigation in relation to this crash. The number of people who have died in this incident makes it one of the worst crashes we've had in a long time. A truck hitting the right pillar door of the car - you can just imagine the impact."
Witnesses to the crash were helping police with the investigation, Mr Hodson said. Some would be referred to Victim Support.
"This is a tragedy - a catastrophic scene - and there will be a number of people who will be affected by this incident."
"We need to recognise that people make mistakes and some crashes are inevitable.
"We don't accept that death and serious injuries from crashes [are] inevitable.
"The message for drivers at this stage is to ensure that if you're going to execute a U-turn, know what's behind you."
NZ Transport Agency's Joint Transport Operating Centre controlled detours along Rosythe Rd and Mountfield Rd, which were still in place at 6pm.