JK Rowling has been advised to settle her court battle over a Harry Potter encyclopedia which came to an end on Wednesday.

US District Judge Robert Patterson Jr, who will decide the case, began the third day of court proceedings by urging the two sides to settle out of court.

On the witness stand, Rowling told the judge that if he allows The Harry Potter Lexicon to be published, it will lead to a number of rip-offs of her books, as well as the work of other popular authors.

A federal judge will decide whether to grant Rowling's request to block publication of the book, based on the fansite by Steven Vander Ark.

Publisher RDR Books has argued that it is little different than any other reference guide to an important novel, and should be allowed to go to press without interference.

It will be weeks before lawyers in the case have finished filing legal documents, and possibly longer before a verdict is rendered.

Earlier in the trial, Vander Ark had described the book as a modest but extensive guide for fans like himself, and not an attempt at serious scholarship.

He wept on the stand during his appearance on Tuesday, saying he had only meant to celebrate Rowling's books, and instead had to live with criticism from other fans.

"Obviously, the best outcome would be an amicable settlement where everybody can be happy and feel that their needs are met. I think that would be terrific," he said outside court on Wednesday.

US copyright law allows teachers, academics, journalists and critics to use excerpts of an author's work, but on a limited basis.

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