The discovery of a dead person on tracks caused all trains across Auckland to be delayed or cancelled ahead of morning rush hour today.
There was widespread disruption across the city's rail network after police revealed the sudden death incident in Manukau overnight.
Heavy fog has also resulted in "multiple crashes" on State Highway 1 Waikato Expressway about 6am - which have now led to a section of the highway being closed in both directions, authorities said just before 8am.
Body found on tracks
The entire Auckland train network has been affected by a police investigation happening south of the city, after a person was found dead on train tracks near Wiri Station Rd.
An investigation was now under way to establish the circumstances of the death, police said.
Train commuters were notified of the widespread delay at 6.30am with a warning to make extra time to travel on public transport this morning.
Auckland Transport said trains on the Southern line between Ōtāhuhu and Pukekohe were cancelled and would run every 20 minutes between Britomart and Ōtāhuhu.
Initially, Eastern line trains were cancelled between Ōtāhuhu and Manukau and would run at 20 minute intervals between Britomart and Ōtāhuhu.
At 7.30am, Auckland Transport said trains were now running all the way to Manukau with rail buses running between Papakura and Pukekohe.
Commuters using trains on the Onehunga and Western lines could expect delays and cancellations.
A spokesman said it would take a while to resume a normal timetable.
Section of SH1 Waikato Expressway closed
Meanwhile, motorists using SH1 Waikato Expressway early this morning are stuck in traffic after at least two crashes in the early hours of this morning.
Emergency services were called to "multiple crashes" on the highway before 6am. One of the crashes, which police said were minor, involved a truck.
It is understood heavy fog was a contributing factor.
St John said they were called to the highway at 4.30am and treated one person who had suffered moderate injuries. They were then taken to Middlemore Hospital in South Auckland.
Shortly before 8am, police issued an alert telling people that the highway at Hampton Downs was now closed in both directions as authorities worked to clear the road.
"This follows earlier crashes along the highway. Motorists are asked to expect delays," a statement said.
Up to two-hour wait in traffic
By 8.45am, road authorities said the highway remained closed, southbound, between Mercer and Te Kauwhata.
Only one lane is open northbound in this area and people are told that it would take "some time" for the vehicle recovery and clean-up effort to be completed.
Again, motorists are being urged to delay their travel.
One driver heading into Auckland told the Herald he had been in traffic for about an hour and 40 minutes.
"It's hectic. I'm coming from Hamilton and have been on the road for coming up to two hours."
Waka Kotahi NZ Transport Agency said there is a detour via SH2 Mangatāwhiri to Okaeria Rd to return to SH1 via Te Kauwhata.
Northbound traffic remains on SH1 - but with one lane open.
"Expect long delays or use alternative route," drivers are told.
Delays on Auckland motorway network
There have also been delays in and around the city's motorway network after a crash and several breakdowns.
NZTA reported a breakdown on SH1 Southern motorway at 8.45am. A vehicle is blocking the left lane, southbound, beside the Grafton Rd on-ramp.
People are being told to pass with care and to expect delays.
A breakdown on the other side of town - on SH20 southwestern motorway - is also affecting the drive into town.
The incident happened just before 9am and is partly blocking the right northbound lane after the Cavendish Dr on-ramp.
A crash was also blocking a lane on the Southern motorway after the Panama Rd overbridge for some time earlier today.