A treasure hunter has taken back a pledge to turn over 500 missing coins minted from gold found in a shipwreck off the South Carolina coast.

The civil trial against Tommy Thompson was put on hold last week when a proposed settlement was reached to deliver the coins to a court-appointed receiver.

However, the deal over the treasure found in the 1857 shipwreck fell apart when the 66-year-old said he had no idea how to obtain the coins.

Former scientist Tommy Thompson is refusing to give up the location of a multi-million dollar treasure. (Delaware County Sheriff's Office)

A Franklin County Commons magistrate had to instruct Thompson, a former scientist, on numerous occasions to answer directly as he testified before the court.

The former scientist claimed a stranger who he couldn’t identify, met him in Fort Lauderdale in 2010 and took the coins but he couldn’t remember the details of the exchange.

He suggested the coins may have been deposited into a trust Thompson had set up in Belize to “keep them safe,” however he can’t be certain.

Thompson discovered the S.S Central America after being funded by over 100 investors. (AP)

Thompson also argued that the trust likely holding the coins would not respond to inquiries because of the ongoing legal proceedings over the treasure.

Thompson found the S.S. Central America in 1988 after convincing more than 100 investors to fund the voyage for nearly $A18 million.

Thompson never repaid the investors and never produced the treasure.

Thompson found coins that were minted from gold bricks found on the S.S Central America. (Odyssey Marine Exploration)

He became a fugitive and fled to Florida before his arrest.

At the time, the value of the treasure was an estimated $A137 million.