NEW York's Attorney General has launched a probe into hundreds of complaints from consumers about prices being increased in the wake of storm Sandy.
Eric Schneiderman said most were about higher fuel prices, but other emergency supplies were also affected.
He said consumers also reported spikes in prices for emergency supplies like generators, hotels raising rates due to demand and higher prices for food and water.
The cost of a bag of potatoes jumped to $7 (£4.40), up from $3 (£1.90) before the storm hit. A box of matches appeared to be more than three times the usual cost, and a loaf was more than double the usual cost.
Around one-quarter of petrol stations are still closed in metropolitan New York.
City authorities said one motorist was arrested after he tried to cut in a long queue at a petrol station and pointed a gun at a motorist who complained.
Retailers were not allowed to charge "unconscionably excessive prices" for goods required for personal, family or household purposes when there was an abnormal disruption of the market.
Mr Schneiderman pledged to do "everything we can to stop unscrupulous individuals from taking advantage of New Yorkers trying to rebuild their lives".
Electricity was returning to New York's neighbourhoods and parts of New Jersey, but many residents in the storm-ravaged area were yesterday said to be still cold, and hungry.
Bruce Springsteen, Billy Joel, Mary J Blige and dozens of other musicians and celebrities helped raise some $23 million for victims of Sandy on an NBC telethon. A Day of Giving on ABC TV networks raised more than $10m.