Iranian president Ebrahim Raisi was laid to rest on Thursday, concluding days of funeral rites attended by throngs of mourners after his death in a helicopter crash, state media reported.

Hundreds of thousands marched in his home town Mashhad to bid farewell to Raisi ahead of his burial following processions in the cities of Tabriz, Qom, Tehran and Birjand.

The 63-year-old died on Sunday alongside his foreign minister and six others after their helicopter went down in the country's mountainous northwest while returning from a dam inauguration on the border with Azerbaijan.

Once the five days of public mourning, announced on Monday, have passed, the authorities including acting President Mohammad Mokhber will focus on organising an election for a new president set for June 28.

Men and women, who were mainly clad in black chadors and clutching white flowers, crowded the main boulevard of Mashhad, the Islamic republic's second city in the northeast where Raisi was born.

Some held aloft placards paying tribute to Raisi as the "man of the battlefield" as a large truck carrying his body drove through the sea of mourners.

"I have come, O king, give me refuge," said a slogan emblazoned on top of the truck, in reference to Imam Reza, the eighth imam of Shiite Islam.

Posters of Raisi, black flags and Shi'ite symbols were erected along the streets of Mashhad, particularly around Raisi's final resting place – the Imam Reza shrine, a key mausoleum visited by millions of pilgrims every year.

Earlier thousands of people holding images of Raisi and waving flags lined the streets of Birjand, capital of the eastern province of South Khorasan, for the procession of Raisi's coffin.

Raisi was South Khorasan's representative in the Assembly of Experts, a clerical body in charge of selecting or dismissing Iran's supreme leader.

Raisi had widely been expected to succeed supreme leader Ayatollah Ali Khamenei, who led prayers in Tehran on Wednesday for the late president and knelt before the coffins of the eight people killed in the helicopter crash.

Among them was foreign minister Hossein Amir-Abdollahian, who was buried on Thursday in the shrine of Shah Abdol-Azim in the town of Shahre Ray south of the capital. (AFP)