Bumper-to-bumper traffic was seen in the streets surrounding two petrol stations this morning after BP announced a surprise free fuel giveaway.

Ormiston Rd BP in Auckland's Flat Bush and the BP at the corner of Woodham Rd and Gloucester St in Dallington, Christchurch let motorists fill up for free between 11am and 12pm as part of an upcoming loyalty promotion.

BP estimated about 500 vehicles filled up for free across the country before the clock struck 12.

Queues in Flat Bush stretched over several kilometres as people tried to take advantage of the giveaway, which was announced just 20 minutes before the pumps opened.

Roadside signs have been posted saying the fuel promotion is over, and traffic is slowly clearing in both suburbs.

Auckland Transport had been pre-warned of the promotion, spokesman Mark Hannan said.

"Our Transport Operations Centre has been monitoring traffic. There have been no issues and the traffic is clearing."

Transport for Christchurch said earlier there was severe traffic congestion in the roads surrounding the BP and warned motorists to avoid the area until it cleared.

Queues stretched for three km outside the Ormiston Rd BP in Flat Bush. Photo / Supplied

According to the latest national fuel prices from AA, a litre of 91 costs $2.259 and a litre of 95 costs $2.349.

BP said it was aiming to get as many cars and motorcycles through the stations to fill up during the hour "as safely as possible".

"We're thrilled to say fuel's on us to the Ormiston and Dallington communities in Auckland and Christchurch," BP managing director Debi Boffa said earlier this morning.

"We regularly develop promotions that give back to our customers and thank them for their loyalty to us, and this is another example of that," she said.

"Our free fuel giveaway is an exciting way to kick off the Fuel on Us promotion, which is designed to celebrate our long-standing partnership with AA Smartfuel and say thanks to our customers who use the programme."

While some lucky motorists got free fuel today, easing global oil prices have also taken the pain out of the pump since March.

Brent crude is selling for about US$65.18 a barrel.

Prices that motorists pay at the pump tend to fluctuate with international oil prices, although other factors (like competition) also play a part in what stations charge.

The average price per litre in New Zealand is still well below the record highs that hit late last year.

In September, the national average price of fuel crept over $2.40 per litre, before dropping off again across November and December.