Three people were left seriously injured in the incident on Marine Drive, Rhos-on-Sea, Conwy county, at about 14:25 GMT on Wednesday.
A black Citroen came off the promenade, down a grassy slope and through iron railings before rolling on to rocks.
Two adults and a teenager, all believed to be women, were taken to hospital.
An adult and teenager were airlifted to Ysbyty Gwynedd in Bangor, Gwynedd, while a second adult was taken by ambulance to Glan Clwyd Hospital, Bodelwyddan, Denbighshire.

Laurence Shahlaei, originally from Cheltenham, took the title in Leeds from two-time title holder Hafthor Bjornsson who is also famed for his role in the popular television series.
Mr Shahlaei, nicknamed "Big Loz", said: "He's a great strongman but it was my day and it felt really good to win."
The 32-year-old is the first Englishman to win the title in 27 years.
Standing at 6ft 2in (1.9m) and weighing 22 stone (145 kg), the Wiltshire-based athlete had to overcome injury last weekend to take the crown.
"I've had a rough few years with injuries and to come back and win Europe's Strongest man has just meant the world to me," he said.
"There's five different events that you have to do. I did a 420 kilo dead lift, which was good enough for joint second and then we did a frame carry - it's a race and you're running a 20-metre course while carrying 450 kilos, which is close to 90 stone, and I won that event."
Competitors also had to lift a 177kg (28 stone) block above their heads "as many times as possible" as well as tackling the infamous Atlas stones - an event synonymous with strongman competitions.
But it was running 20m (65ft) with a Volkswagen Beetle on his shoulders in around 11 seconds that clinched the title from Iceland's Hafthor Bjornsson.
"My favourite of the competition was the car walk.  Imagine Fred Flintstone running in his car - that was basically me," he said.
"I actually broke the world record on that event.  They made the car even heavier this year and I managed over a second off my world record - which was really, really good."

The teenager was walking on the Ancrum Road crossing, near the junction with Ancrum Drive, when she was hit by a black Ford Fiesta at about 17:20 on Monday.
She is receiving treatment at Ninewells Hospital.
Police Scotland have appealed for witnesses to contact them.

The price of Brent crude oil fell below $39 a barrel at one point, its lowest since December 2008.
The IEA said demand in the current quarter was growing by 1.3 million barrels a day, down from 2.2 million barrels in the previous quarter.
The IEA predicts that will slip back to 1.2 million barrels a day next year.
The price of Brent crude fell to $38.90 a barrel at one point, before recovering slightly to $39.13 - still down 60 cents in the trading session. US crude oil also fell, down 50 cents to $36.12 a barrel.
Oil prices are down more than 10% over the week. The trigger was a meeting of oil producers' cartel Opec late last week, which broke up in disarray as the member countries failed to agree to put a lid on production.
Opec producers pumped more oil in November than in any month since late 2008, almost 32 million barrels per day. That comes at a time when the world's economic growth is slowing, blunting demand for raw materials.
The IEA said that although consumption was likely to have peaked in the third quarter, demand growth of 1.2 million barrels a day was still healthy.
Earlier this week, the US Energy Information Administration forecast that US shale oil production, now a major source of oil supply, would fall in January for the ninth month in a row.
Sustained falls in output could help to stabilise the price of oil, although some market forecasters suggest the price could continue to fall to as low as $20 a barrel.
A woman has been arrested on suspicion of dangerous driving after a car crashed through a seafront barrier and fell on to rocks.
[NEXT_CONCEPT]
Game of Thrones star "The Mountain" has been beaten to Europe's Strongest Man title by a man from Swindon.
[NEXT_CONCEPT]
A 15-year-old girl has suffered a serious head injury after being hit by a car on a pedestrian crossing in Dundee.
[NEXT_CONCEPT]
The oil price has fallen to a new seven-year low after the International Energy Agency (IEA) forecast a slowdown in growth in demand for oil.