U.S. President Barack Obama's campaign has taken its first hard swing at Mitt Romney with a biting new TV ad that portrays the Republican as a "vampire."

A young Mitt Romney is seen during a documentary-like ad campaign endorsed by U.S. President Barack Obama. (BarackObama.com) Romney, who is the presumed Republican presidential candidate, spent years as a venture capitalist.

His company's business practices are front and centre in the documentary-like video, a version of which will air on television Wednesday for the first time in five key states. A six-minute online video, dubbed Romney Economics, has garnered over 200,000 views since Monday.

The ad features testimonials from workers laid off at a Kansas City steel plant, which was bought and then closed down by Bain Capital — the firm Romney headed for 15 years.

"It was like a vampire. They came in and sucked the life out of us," said Jack Cobb, identified as a steel worker for 31 years.

"It was like watching an old friend bleed to death," added another worker.

"What Bain Capital did was not capitalism, it was bad management," said Dave Foster, the lead negotiator for workers at GST Steel, adding that Romney was deeply involved in the way the company was run.

"The business model of loading a company up with debt in order to extract immediate profits for yourself out of it, and then ensuring the failure of the company later on, seemed like exactly the wrong thing we need in America today," he added.

Ad has harder edge than hope campaign

The ad's sombre tone is a striking change from Obama's 2008 campaign for hope and change.

It may invite viewers to imagine Romney with fangs, but it also aims to de-fang his economic credentials, which Romney has often touted as his greatest strength.

Workers describe the way Bain was "sucking money out of the company" and how they view Romney as a "job destroyer."

Romney has thus far ignored the attack, but his campaign quickly produced its own counter-ad on jobs at a Bain-owned steel plant that's still in business.

The sunnier Republican ad argues that when others shied away, Romney's private sector leadership team stepped in. It features steel workers who say the number of jobs have grown in their hometown.

"One of the hardest things to do is move up a socio-economic status in a generation," says one man. "Because of this company, I'm able to do that with my family."