At least 21 people have died and more than 120 are injured after an underground train derailed in the Moscow metro during morning rush hour.

Rescuers are still trying to recover bodies after the accident 85 metres below ground on the world’s busiest subway system.

Scores were injured after a suspected power surge caused the train to stall and several cars to come off the rails in one of the worst accidents in the Russian capital’s subway system in years.

Three carriages derailed between Slaviansky Boulevard and Park Pobedy stations in the west of the city, while travelling at 70 kilometres per hour about 8:35am local time.

Russian president Vladimir Putin, who is away in Brazil, ordered a criminal investigation into the accident, which is likely to raise further questions over Russia’s transport safety record.

There was no suspicion of a militant attack – the cause of scores of deaths in Moscow’s subway system in years past.

About 60 ambulances were stationed at the scene.

Rescue workers evacuated more than 1,000 people from the area of the accident, the emergencies ministry said.

Russian news agency Itar-Tass quoted health ministry representative Oleg Salagai as saying that 129 people were injured, 42 of whom were in a serious condition.

Bloodied passengers helped by emergency service workers

Injured passengers were carried bloodied and bandaged out of stations and helicopters ferried the most seriously hurt to hospitals across the city.

Passengers looked stunned or were crying after being helped to the surface by emergency services.

They described an abrupt stop thought to be caused by a sudden power surge.

“There was an abrupt deceleration, the lights went off then there was a spark of fire and smoke, we were blocked in,” said one passenger.

“I was in one of the carriages, I felt a sudden shock and fell down, all the people were lying side by side on the floor. I cannot speak for the others, I was in the front carriage, the carriages were not very full but there were enough people there.”

Russia’s investigative committee said it was looking into the causes of the accident.

The committee, which answers to Putin, said it had opened a criminal case on suspicion of failure to meet safety guidelines but that it had not yet determined the cause of the accident

Critics have accused the Moscow government of spending too much on extending the underground network and not enough on maintenance.

“There is no one alive left,” Moscow’s deputy mayor Peter Biryukov said. “The cause is not known, the work continues.”

Mr Biryukov said bodies were recovered from the wreckage, but that some remained underground.

Bodies remain underground as investigators search for answers

Television footage showed rescue workers carrying the injured away on stretchers, while paramedics treated some on nearby grass verges.

“It braked very hard. The lights went off and there was lots of smoke,” a man at the scene told Rossiya-24 television.

“We were trapped and only got out by some miracle. I thought it was the end.

“Many people were hurt, mostly in the first rail car because the cars ran into each other.”

A city transport services spokesman told news agency Interfax that all passengers had been evacuated from the affected stations, dismissing reports that some passengers were still trapped in the tunnel.

Moscow mayor Sergei Sobyanin was at the scene and pledged to do everything possible to help the victims.

Russians regularly criticise the country’s transport safety record. Recent disasters included the 2011 sinking of a ferry boat that killed 128 and an airplane crash that killed the Lokomotiv Yaroslavl ice hockey team the same year, both of which were blamed on lax safety regulations and technical errors.

On weekdays as many as 9 million people use Moscow’s subway system.

Famed for its high-vaulted halls adorned with Soviet socialist realist art, the underground network has expanded from 13 stations opened in 1935 to 194 stations across the megalopolis today.

Islamist militants have previously carried out deadly attacks in Moscow, including twin suicide bombings that killed 40 people on the subway in 2010.