Harrisburg area officials unveiled their proposal Thursday to lure Amazon's new headquarters, and its promised 50,000 new jobs, to central Pennsylvania.

Mock-ups of a sprawling campus at the old Harrisburg State Hospital site were made public but the actual proposal--and a possible tax credit package--remain secret.

"We're in competition," said David Black, president of the Harrisburg Regional Chamber & CREDC. "We don't want to tip our hand."

Dozens of cities and regional development authorities submitted their proposals Thursday, the deadline set by Amazon. Pennsylvania faces stiff competition, including a number of multi-billion-dollar tax credit packages organized by states like New Jersey.

J.J. Abbott, a spokesman for Gov. Tom Wolf, said the governor spoke with a senior executive at Amazon and sent a letter to CEO Jeff Bezos in an effort to draw the world's third-largest tech company to the state.

The contents of any incentive package would not be released, at least not on Thursday, according to Abbott.

READ MORE: Pa. cities rush to clinch the lucrative Amazon deal

Tax credits offset the amount a company--in this case, Amazon--would otherwise owe, effectively shifting the burden of paying for infrastructure the company uses onto other taxpayers. The hope is that the money will be recouped through other economic activity that would not have existed without the tax credit, such as personal income tax paid by Amazon's new hires.

When told of New Jersey's $7 billion Amazon tax credit package, Black said: "Wow. I did not know that."

He added, when asked if the state could compete with that level of spending, "I believe Pennsylvania is competitive."

No existing state tax credit program would be able to cover such an incentive package, Black said.

In effect, New Jersey's $7 billion proposal would spend $140,000 per job. According to the government subsidy tracking organization Good Jobs First, government entities should spend no more than about $50,000 per job in order to break even.

According to Amazon's bidding documents, it plans to invest roughly $5 billion in infrastructure and construction.

Black said he's optimistic about Harrisburg's chances and he hopes to at least bring Amazon to the area to look at the site. If the proposal isn't successful, he said, the process still provided a learning experience.

"Unless you try to do things, nothing's going to change," he said.

The state hospital proposal, which is located predominantly in Susquehanna Township, would call for the construction of a number of high-rise buildings, the tallest of them 12 stories tall. Black said preparing the proposal and the site drawings cost about $10,000 and untold staff hours.

Black pointed to Penn State University, located roughly an hour north of Harrisburg in Centre County, as one way to satisfy Amazon's requirement for a nearby research university. And Harrisburg International Airport could add flights to the west coast if Amazon comes to Dauphin County, he said.

Dauphin County Commissioner Jeff Haste pointed to the area's low cost of living and high quality of life as potential drivers to lure Amazon.

"I hope, in a few months, we're back here for the ribbon cutting," he said.

Susquehanna Township Commissioner Frank Lynch said it was worthwhile "to try to grab a star like Amazon." And Jackie Parker, Harrisburg's director of community and economic development, said: "Everything you could want is right here and we didn't even have to use any gimmicks like Tucson--bringing in a cactus."

Wallace McKelvey may be reached at wmckelvey@pennlive.com. Follow him on Twitter @wjmckelvey. Find PennLive on Facebook and YouTube.