More than 20 people were injured as two metro trains collided in the Iranian capital Tehran on Wednesday.

The accident occured on the Line 5 of the Tehran metro on the Karaj-Golshahr railway when a high-speed train enroute to Sadeqieh station hit a slow-moving local train near the Chitgar station. Line 5 of the metro stopped operating after the incident.

Mojtaba Khaledi, the spokesman for the national emergency services, said that 22 people sustained injuries in the incident and ambulances that were dispatched to the site of the accident transferred 11 people to nearby hospitals. Two of of the injured are in critical conditions. He added that about 20 other people had been stuck in the wagons but were moved out by rescue workers.

Tehran Mayor Alireza Zakani said there are some speculations about the cause of the collision, but further investigation is needed to find out exactly how it happened.

According to Mojtaba Shafi’i, the deputy for transportation in Tehran’s municipality, the wagons are being removed from the railway so that the lines become operational as soon as possible, suggesting that trains can be back on track about noon.