Dhaka, Oct 23 : At least 20 persons were killed while 50 others were injured after a cargo train collided with a passenger train in Bhairab Upazila outskirt of Dhaka in Bangladesh on Monday. Mohammad Ferdous, officer Incharge of Kamalapur Railway Police told IANS that two relief trains have reached Bhairab and have started the rescue operation. He said that the fire service personnel have also been put in the emergency relief work to rescue the injured. He said that the immediate cause of the collision was not known and a probe has been launched into the incident. The collision took place after two rear coaches of the Dhaka-bound Egarosindur Godhuli Express passenger train was hit by a cargo train heading to Chattogram, Azizul Haque Rajon. Train collision is common in Bangladesh due to the unsupervised railway crossings, poor signaling and official negligence. The police officials said that people are still trapped under the debris and the rescue operation is going on. Mosharraf Hossain, Fire and Service official, said that the locals too have joined the rescue operation. He said at least 20 dead bodies have recovered so far and that the number of casualties can increase. 'Four units of the Fire and Services are currently doing the rescue operation. It is a chaotic situation,' Mosharraf Hossain told IANS. Bhairab Station Master Yusuf said that the rail connectivity from Dhaka to Chittagong; Dhaka to Sylhet; Mymensingh to Chittagong; Sylhet to Kishoreganj remained suspended following the accident for more than four hours. /IANS