They follow an admission by the world?s biggest carmaker that it deceived US regulators in exhaust emissions tests.
A DoJ criminal investigation would be serious, as federal authorities can bring charges with severe penalties against a firm and individuals.
Late on Tuesday, New York state?s top lawyer announced an investigation.
New York Attorney General Eric Schneiderman said he would collaborate with other states to enforce consumer and environmental law.
?No company should be allowed to evade our environmental laws or promise consumers a fake bill of goods,? Mr Schneiderman said in a statement announcing the probe.
Meanwhile the Environmental Protection Agency and the California Air Resources Board are investigating the way VW cheated tests to measure the amount of pollutants coming from its diesel cars.
Volkswagen said 11 million vehicles worldwide were involved and it was setting aside ?6.5bn (?4.7bn) to cover costs of the scandal.
According to news agencies Bloomberg and AFP, the DoJ is looking into the issue, which raises the possibility of the company and individual executives facing criminal charges.
However, the DoJ often extracts hefty payments from companies to settle criminal charges.
?Totally screwed-up?
Volkswagen is due to hold a supervisory board meeting on Friday.
But reports say that chief executive Martin Winterkorn will appear before a select group of board members before then, possibly later on Wednesday.
On Tuesday, Mr Winterkorn issued a fresh apology for the test-rigging, saying he was ?endlessly sorry? for the ?manipulation?.
The boss of Volkswagen?s US business, Michael Horn, has also admitted the firm ?totally screwed up?.
In the UK, the Department of Transport has added its voice to calls for an EU-wide investigation into the affair.
VW shares are down 30% so far this week.
Fines looming
Last Friday, the US Environmental Protection Agency (EPA) said VW diesel cars had much higher emissions than tests had suggested and that software in several diesel cars could deceive regulators.
As a result Volkswagen was ordered to recall half a million cars in the US.
The EPA found the ?defeat device?, the device that allowed VW cars to emit less during tests than they would while driving normally, in diesel cars including the Audi A3 and the VW Jetta, Beetle, Golf and Passat models.
VW has stopped selling the relevant diesel models in the US, where diesel cars account for about a quarter of its sales.
The EPA said that the fine for each vehicle would be up to $37,500 (?24,000). With 482,000 cars sold since 2008 involved in the allegations, it means the fines could reach $18bn.
That would be a considerable amount, even for the company that recently overtook Toyota to be the world?s top-selling vehicle maker in the first six months of the year.
Industry experts are concerned about what this means more widely for diesel car manufacturers.
Jim Holder, editorial director of Haymarket Automotive, whose titles include WhatCar and AutoCar, told the BBC that there had never been a scandal in the industry of this size, and that it could make diesel engines for cars uneconomical.
Martin Leach, a consultant at Magma and a former head of Ford Europe, says the problem is unlikely to emerge elsewhere: ?I don?t think it will extend to other manufacturers. Volkswagen has really engaged to try to beat standards in the US. I would be surprised if it spreads outside the US as Europe?s testing standards were more advanced and therefore more difficult to cheat than the US.?
BBC
