At least 21 people were killed and dozens injured on Wednesday when a train derailed near the central Iranian city of Tabas after hitting an excavator.

The train was on its way from the northeastern city of Mashhad to the central city of Yazd with 348 passengers on board when it careered off the track in the desert at 5:30 am (0100 GMT).

A passenger train traveling through eastern Iran struck an excavator and derailed nearly half its cars before dawn Wednesday, killing at least 21 people and injuring 87, officials said.

The train operated by the state-run Islamic Republic Railway carried some 350 people as it travelled from Tabas, 550 kilometers southeast of Tehran, to the city of Yazd. The route began as an overnight train out of Iran's holy city of Mashhad.

Yazd province’s emergency organisation chief Ahmad Dehghan said 21 people were killed in the incident, according to the website of state broadcaster IRIB, revising an initial death toll of 17 given by national authorities.

The deputy head of Iran’s state-owned railways, Mir Hassan Moussavi, told the state broadcaster that the train was carrying 348 passengers.

It “derailed after hitting an excavator” that was near the track, he said.

Rescue teams inspected the overturned carriages as onlookers gathered nearby, pictures posted by the ISNA news agency showed.

One of the pictures showed a yellow excavator on its side by the track.

Five of the train’s 11 coaches came off the rails, the Iranian Red Crescent’s head of emergency operations, Mehdi Valipour, told state television.

President Ebrahim Raisi expressed his grief over the derailment and offered his condolences to the families of the dead.

He also issued orders for a speedy investigation into the causes of the crash, his officer said.

Roads and Urban Development Minister Rostam Ghassemi apologized to Iranians on Twitter and said the ministry was responsible for the incident.

“Hitting the excavator was the main cause of the accident,” Ghassemi said, adding that initial reports indicated that the driver only braked after hitting the obstructing vehicle.

“What is clear is the human error, which is more on the part of the driver, and why and how should be investigated more closely,” he stressed.

Iran's President Ebrahim Raisi offered condolences over the crash and announced an investigation would be undertaken into its causes.

Iran's worst train disaster came in 2004 when a runaway train loaded with gasoline, fertilizer, sulfur, and cotton crashed near the historic city of Neyshabur, killing some 320 people, injuring 460 others, and damaging five villages. Another train crash in 2016 killed dozens and injured scores of people.