The 36-year-old from Carrickfergus had been level on 15 with the late Robert Dunlop going into Thursday's races.
Seeley broke away to win the opening Supersport race ahead of runner-up Ian Hutchinson and Martin Jessopp.
The Supertwins race was abandoned after a two riders were injured in a high-speed crash.
Dungannon rider Ryan Farquhar and Dan Cooper from Stroud came off at Black Hill and were taken to hospital.
Forty-year-old Farquhar sustained chest and pelvic injuries, while Cooper, 28, had shoulder injuries.
Record-breaker Seeley has won at least one event at the North-West for nine years in a row.
He has also won at least one Supersport race in each of seven consecutive years from 2010 to 2016.
The Supersport event provided a thrilling start to racing at the 2016 North West.
Ballymoney's Michael Dunlop, a four-time winner at the North West, did not make it off the grid because of mechanical problems.
Seeley surged into an early lead but some exillerating action saw Fermanagh rider Lee Johnston, Yorkshire man Hutchinson and Michael's brother William Dunlop all take turns at the front.
Seeley, Hutchinson and Jessopp all broke the class lap record on the final circuit.
"The North West put me on the map when I first came here and now to be mentioned in the same sentence as the Dunlops is unbelievable," said an elated Seeley.
"It was a typical Supersport race. We managed to get a break and clinch the 16th win."

Dozens of soldiers seized the parliament compound in the administrative capital Garowe and blocked nearby streets.
However one of the region's most respected clan elders, Islan Issa Islan Mohamed, told them to return to their barracks.
He told the BBC that the "drama" was now over.
It had been reported that the soldiers were protesting about a delay in the payment of salaries as well as poor working conditions.
Last September soldiers took control of the central bank in Garowe in protest at lack of payments, Garowe Online reported.
Puntland profile
Puntland, an arid region of north-east Somalia, declared itself an autonomous state in August 1998, in part to avoid the clan warfare engulfing southern Somalia.
Unlike its neighbour, breakaway Somaliland, Puntland says it does not seek recognition as an independent entity, wishing instead to be part of a federal Somalia.

30 March 2017 Last updated at 22:18 BST
But amateur artist Emanuel Santos, who works at Madeira airport where the bust was unveiled, says he feels hurt by the criticism his work has received.

The former "It Girl" and reality TV star said she began receiving treatment in January for a non-malignant growth in her pituitary gland.
Ms Palmer-Tomkinson, 44, told the Daily Mail: "I got terribly frightened. I started thinking, 'I'm going to die.'"
The tumour has been successfully reduced by the treatment, she said.
Ms Palmer-Tomkinson said the tumour was discovered after she went for blood tests after feeling ill in the summer of 2015.
She said: "'I actually feel very lucky. My growth was non-malignant but it affected the production of prolactin. I've been with people who have malignant brain tumours so I don't want to be like, 'Hey look at me'.
"I have been - touch wood - luckier. I've taken medication and, thankfully, it seems to have gone away for now."
The pituitary is a pea-sized gland on the underside of the brain which controls the release of hormones in the body.
A prolactinoma is normally a benign, slow-growing tumour in the pituitary gland, but its effect on the secretion of the hormone prolactin can cause infertility.
Ms Palmer-Tomkinson was also diagnosed with an auto-immune condition, which causes tiredness, joint pain and acute anaemia.
Having been treated for cocaine addiction in the past, she has criticised media coverage which had blamed her frailty on drugs.
"That's always their take on it... cocaine. That was so many years ago. But not many people can contemplate Tara's life without it," she said.
Alastair Seeley has broken the record for wins at the North West 200 road races by achieving his 16th career win at the international meeting.
[NEXT_CONCEPT]
Troops in Somalia's semi-autonomous region of Puntland have briefly staged a mutiny.
[NEXT_CONCEPT]
A bronze bust of Cristiano Ronaldo has made headlines around the world for its lack of resemblance to the Real Madrid star.
[NEXT_CONCEPT]
Socialite Tara Palmer-Tomkinson has revealed that she feared she was going to die when she learned she had a brain tumour.