A US judge is to rule whether five performing killer whales have the same constitutional rights against slavery as human beings.

US District Judge Jeffrey Miller called the hearing in San Diego after Sea World asked the court to dismiss a lawsuit filed by People for the Ethical Treatment of Animals that names the five orcas as plaintiffs in the case.

Peta claims the captured whales are treated like slaves for being forced to live in tanks and perform daily at its parks in San Diego and Orlando, Florida. "This case is on the next frontier of civil rights," said Peta's lawyer Jeffrey Kerr, representing the five whales.

Sea World's lawyer Theodore Shaw called the lawsuit a waste of the court's time and resources. He said it defies common sense and goes against 125 years of case law applied to the Constitution's 13th amendment that prohibits slavery between humans.

"With all due respect, the court does not have the authority to even consider this question," Mr Shaw said, adding later: "Neither orcas nor any other animal were included in the 'We the people' ... when the Constitution was adopted."

Judge Miller listened to both sides for an hour before announcing that he would issue his ruling at a later date.

The judge raised doubts a court can allow animals to be plaintiffs in a lawsuit, and he questioned how far the implications of a favourable ruling could reach, pointing out the military's use of dolphins and scientists' experiments on whales in the wild.

Mr Kerr acknowledged Peta faces an uphill battle but he said he was hopeful after the hearing.

"This is an historic day," he said. "For the first time in our nation's history, a federal court heard arguments as to whether living, breathing, feeling beings have rights and can be enslaved simply because they happen to not have been born human. By any definition these orcas have been enslaved here."

The issue is not about whether the animals have been subjected to abuse, the defence said. If the court were to grant orcas constitutional rights, Shaw warned the ruling would have profound implications that could impact everything from the way the US government uses dogs to sniff out bombs and drugs to how zoos and aquariums operate. "We're talking about hell unleashed," he said.

Peta said a ruling in its favour would only help to protect the orcas in the entertainment industry and other cases involving animals would have to be decided on their own merits.