People look out of the window as a huge inflatable "Superman" passing by during the Balloon Day Parade in Brussels, Saturday, Sept. 7, 2013. The giant balloons in the form of comic book and cartoon heroes are parading as part of the "Comic Book Festival". (Xinhua/Gong Bing)

NEW YORK, March 3 (Xinhua) -- Rare copies of comic books dating back to the mid-1930s in which Superman and Batman made their first appearances are to be auctioned in May in Connecticut, U.S., local media said on Friday.

The copies of the 1938 Action Comics No. 1, in which Superman makes his debut, and the 1939 book Detective Comics No. 27, which features the first appearance of Batman are among over 18,000 books and 300 pieces of comic-book art collected by Jon Berk, an attorney in Connecticut.

The Hartford lawyer, 66, who started to hunt comics when he was in law school at Boston University, said it is time for someone else to enjoy the books.

Photo taken on Oct. 9, 2010 shows Michael Keaton's costume in Batman Returns at the Legends Auction in Macao, south China. The costume was sold at a price of 35,000 US dollars. Julien's Auction held this auction featuring pop culture artifacts from the Beatles, Elvis, Madonna, Bruce Lee, Princess Diana, Michael Jackson and other iconic legends whose popularity spans all continents. (Xinhua/Cheong Kam Ka)

Berk's collection goes on display on March 11 at the Metropolis Gallery in New York City. It goes to auction online May 15 at ComicConnect.com.