Guillermo del Toro

Director Guillermo del Toro and star Charlie Hunnam on the set of "Pacific Rim." (Kerry Hayes / Warner Bros. / November 16, 2011)

Get ready for giant monsters vs. colossal robots, Round 2: Writer-director Guillermo del Toro is working on a script for a sequel to his 2013 sci-fi film "Pacific Rim."

"I'm working very, very hard with Zak Penn," Del Toro told BuzzFeed at the Austin Television Festival over the weekend. "We've been working for a few months now in secret. We found a way to twist it around."

Del Toro added that finance and production company Legendary Pictures has not formally agreed to make the film, but that he and Penn ("X-Men: The Last Stand," "The Incredible Hulk") are writing the script as if it will see the light.

"I don't have the money, but I'm proceeding like it is happening," Del Toro said, adding that he hopes to make "Pacific Rim 2" after his next producing project.

Released last July, the original "Pacific Rim" tells the story of a future in which giant monsters called kaiju have emerged from an undersea portal and begun laying waste to coastal cities. To fight back, the military creates 25-story robots operated by two pilots who control the machine via a psychic bond.

The $190-million film did only moderate business in the U.S., where it just crossed the $100 million mark, but it earned positive reviews and also flourished overseas, taking in an additional $309 million.

Back in April, discussing the possibility of a sequel, Legendary principal Thomas Tull told The Times, "We love ['Pacific Rim'] and we love working with Guillermo del Toro. We would continue working on it, but we wouldn't do it just to do it."

Del Toro said the sequel script picks up where the first movie left off and includes the characters Raleigh Becket (Charlie Hunnam) and Mako Mori (Rinko Kikuchi).

"Some people were wondering if we were going to do the prequel," Del Toro said. "I was never interested in doing that first wave of invasion. I'm going for very new, very crazy ideas on the second one, which are very different from the first one — but you will get really great spectacle."

Times staff writer Steven Zeitchik contributed to this report.