Guards at the UN war crimes tribunal have removed Ratko Mladic from court after the former Bosnian Serb army chief harangued the judge reading out the charges and entering a not-guilty plea for Mladic.

Having threatened to boycott his second hearing since being tracked down and extradited from Serbia to The Hague in May, Mladic did appear but demanded new legal representation and sought a delay in filing his plea.

He also complained of cold after being told not to wear his cap.

Judge Alphons Ourie rejected his request for a postponement but said the tribunal would check if the Serbian and Russian lawyers he wants would be allowed to replace the attorney the court appointed for Mladic.

When Ourie moved on to rule that, in the absence of a plea, the court would enter one for Mladic after reading out the charges, the 69-year-old former career soldier shouted: "No, no, no! Don't read it to me, not a single word."

As Ourie pressed on, warning Mladic that he would be removed if he interrupted again, he stated the first charge as genocide.

"No, no, I'm not going to listen to this without my lawyer," Mladic shouted as he removed his translation earphones. "You are no court.

"Who are you? You're not allowing me to breathe."

The judge adjourned the hearing, screening it off from public view, before resuming minutes later with an empty dock to read the remaining charges, formally entering a not-guilty plea after each one. There are 11 charges.

Mladic is accused over the 43-month siege of Bosnian capital Sarajevo and the Srebrenica massacre of 8000 Muslim men and boys, Europe's worst massacre since the Second World War.

He was represented by court-appointed lawyer Aleksandar Aleksic, who asked for the plea hearing to be delayed and to be allowed to leave if Mladic did not want him there.

Mladic has asked for Belgrade-based military lawyer Milos Saljic and Russian jurist Alexander Mezyaev to represent him.

The court is verifying their qualifications and eligibility.

Mladic was arrested on May 26 after 16 years on the run. He said the charges against him were "obnoxious" and "monstrous" when he was formally charged at the war crimes court on June 3.

At the start of the hearing, Judge Orie repeatedly asked Mladic to stop interacting with the public gallery, where families of Srebrenica victims were seated to Mladic's right.

"I hear better on my left ear," Mladic replied, suggesting he was turning his head to the judge only to hear him better.

Without the cap he wore at this first hearing, Mladic, who claims he is "gravely ill", barked at the judge and complained he was "an old man".

"I have to wear a cap because I am too old, and I am cold. One side of my body is not functioning," he said, possibly referring to the effects of a stroke.

"I want to communicate with you in a humane way. You are trying to impose impossible conditions on me, a lawyer I don't want."