ISLAMABAD, Nov. 3 (Xinhua) -- At least 21 people were killed and 45 others injured when two passenger trains collided with each other in Pakistan's southern port city of Karachi on Thursday morning, hospital officials said.

Spokesperson of the Jinnah Hospital of Karachi, Seemi Jamali, said that so far 21 bodies and 45 injured have been brought to the hospital.

At least two children and three women are among the deceased persons, Jamali said.

Deputy Superintendent of Pakistan Railway, Nasir Aziz, said that the incident took place when a passenger train Farid Express collided with another passenger train Zakria Express near Qadafi Town area of the city.

"According to initial information, Farid Express was waiting for its clearance at the Qadafi Town railway station and Zakria Express coming on the same track from the same direction hit it at the backside when its driver failed to stop his train despite red signal," said Aziz.

Earlier, Aziz said signalman failed to divert the Zakrai Express to the other track.

Both trains were coming from the country's eastern province of Punjab.

The railway official said an investigation would be launched to know the real reason behind the accident.

The railway traffic has been suspended completely till the completion of the rescue work, the railway official said.

Three coaches of the Farid Express were destroyed completely while two others were damaged partially in the accident.

Rescue workers are still busy in cutting into one of the coach to rescue a passenger who had been trapped inside.

According to the hospital official, the death toll may further rise as several injured are in critical condition at the hospital, who suffered severe head and neck injuries.

Personnel of engineering unit of Pakistan army have also reached the site with heavy machinery for rescue work and to clear the track.

Pakistani Prime Minister Nawaz Sharif expressed his sorrows over the loss of the precious lives and directed the authorities concerned to provide the best available treatment to the injured.