A member of the public who contacted the Herald last night said he and his family had just passed the crash site and that traffic was backed up, as a result.
"The trailer is still attached to the truck. Half of it is sticking out of the road."
In the early hours of this morning, two people had critical injuries and one was in a serious condition after a crash north of Auckland.
Four ambulances rushed to the scene on Whangaripo Valley Rd near Wellsford just after 1am.
The injured have been taken to Auckland City Hospital.
In the South Island, two people were injured in Otago after the car they were in flipped.
Southerly wind could also be strong at times in exposed places today, but "most people [in Wellington] wouldn't think it's particularly windy today," Ms Flynn said.
Tomorrow would be similar but "a little nice".
"People might see a bit more sun," she said.
Monday should be mainly fine.
"Again, there's a gradual improving trend," she said.
Cloud was expected to increase in Christchurch today with chances of patchy drizzle.
A team that included safety engineers were on standby to raise the flag since dawn, but wind speeds on the bridge have been around 37 knots, the New Zealand Transport Agency said.
Anything higher than 20 knots is deemed to be unsafe for staff and could also risk the flag ripping and causing hazards for traffic.
All flags were now removed.
The weather is being monitored and at this stage a further attempt to raise the flag would be made around lunch time.
Motorways are expected to be yet again busy for the long weekend, particularly, on State Highway 1 between Puhoi and Wellsford.
"...It then gets very busy again on Saturday from about 8.30am, with the heaviest peaks lasting from 9am all the way through until 2.30pm," NZTA Auckland and Northland Highway manager Brett Gliddon said.
"For those heading south on SH1 and on SH2 through Maramarua, there'll be heavy traffic from lunchtime Friday, with the busiest peak from 2pm until early evening."
Aucklanders heading home on Sunday and Monday should expect delays from lunch time until 5pm both days, Mr Gliddon said.
"Motorists returning to Auckland from the south on SH2 and SH1 can expect the busiest times on Monday from the middle of the day, so travel early to avoid delays," he said.
Mr Gliddon said drivers who wanted to spend less time being on the road should avoid travelling during peak times.
A NZTA spokeswoman advised drivers to allow plenty of time to travel as delays are expected.
NZTA tips for safe driving:
• Ensure everyone travelling with you is wearing a seatbelt