At least 21 people have been killed and 45 injured when two passenger trains collided in Pakistan's southern port city Karachi.

Officials said at least two children and three women were among the dead. The collision happened early Thursday morning, when a train carrying hundreds of passengers crashed into the back of another. A hospital official said some of the injured were in a critical condition and the death toll may rise.

Photo taken on Nov. 3, 2016 shows the rescue work at the site of a collision between two trains in southern Pakistani port city of Karachi. [Photo/Xinhua]