The hike, announced the same day, had been widely expected after Vietnam devalued its currency early this month for the fourth time since late 2009, pushing up the cost of imported fuel.

Vietnam subsidises petrol prices to offset the effect of rising oil prices, which hit two-year highs on world markets in Asian trade Thursday as turmoil continued in the Middle East.

Another key consumer commodity, electricity, will increase in price by 15 percent in Vietnam next month, official media said this week.

Hundreds of motorbike riders and motorists had waited at one central Hanoi petrol station hoping to beat the mid-morning price rise, which also saw the cost of diesel shoot up about 24 percent.

But many left disappointed after the government-set petrol price jumped from 16,400 dong (78 cents) to 19,300 dong per litre before they could buy.

"Obviously, the rise in petrol prices will lead to increases in other sectors like transport," said Do Tuan Khang, 42, an army officer waiting to fill up his motorbike.

"That's going to aggravate the country's inflation, which is already worrying a lot of people."

Inflation in Vietnam has accelerated every month since August 2010, hitting 12.17 percent year-on-year in January, far higher than its neighbours.

To help control prices, Prime Minister Nguyen Tan Dung has vowed to cut state spending by 10 percent through measures including the delay of non-essential projects, the official Vietnam News reported Tuesday.

Pham Chi Lan, a former government adviser, said keeping prices under control would be difficult and a 10 percent cut in expenditure would not be enough because of inefficiency in the large state sector.