Egypt's former president Mohamed Morsi was buried in Cairo on Tuesday, his lawyer said, a day after he collapsed in court and died.

State TV said the 67-year-old's death was due to a cardiac arrest.

"He was buried in Medinat Nasr, in eastern Cairo, with his family present," said Abdel Moneim Abdel Maksoud, one of his lawyers. 

Morsi had appeared animated during a hearing in a retrial over charges of collaborating with foreign powers and militant groups, judicial and security sources said.

"The court granted him his request to speak for five minutes... He fell to the ground in the cage... and was transported immediately to the hospital. A medical report found... no pulse or breathing," said the attorney general's office.

"He arrived at the hospital and dead at 4:50 pm exactly and there were no new, visible injuries found on the body."

Another Morsi's legal defense team described the moment he received news of his death.

"We heard the banging on the glass cage from the rest of the other inmates and them screaming loudly that Morsi had died," the lawyer, Osama El Helw, told AFP.

Since Morsi's overthrow on July 3, 2013, his former defense minister, now President Abdel Fattah al-Sisi, has waged an ongoing crackdown that has seen thousands of Muslim Brotherhood supporters jailed and hundreds facing death sentences.

A judicial source said Morsi had fainted during a break in the trial hearing.

The court officials "had just finished the session for the espionage case and they informed the judge that he had fainted and needed to be transported to a hospital where he later died," he told AFP.

Morsi last saw his family in September 2018. A month later, one of his sons, Abdallah, was arrested.

Turkish President Recep Tayyip Erdogan, a strong ally of Morsi, paid tribute to the "martyr."

The Gaza-based Palestinian movement Hamas also hailed Morsi's influence.

Iran's Foreign Affairs Ministry spokesman Abbas Mousavi called his death "sad and unfortunate" and said that "while respecting the views of the great nation of Egypt, offers its condolences."