WASHINGTON - Two Metro transit trains collided at the height of the Monday evening rush hour, killing at least four people and severely injuring others as cars of one train jackknifed into the air and fell atop the other. One of the fatalities was a female train operator, Metro officials say. The six-car train derailed and then collided with another train on an elevated track between the Takoma Park and Fort Totten stations around 5 p.m. Monday, trapping dozens of passengers. Some reports indicate as many as 50 people are injured. The trains are "lodged on top of one another," D.C. Fire and EMS spokesman Alan Etter says. Officials are preparing for a "mass casualty event," Etter says. Rescue crews were using heavy duty equipment to cut the train apart to rescue at least 100 people who were trapped, officials say. The extrication process appeared to be over just before 7 p.m. Rescue workers propped steel ladders up to the upper train cars to help survivors escape. Seats from the smashed cars had spilled out onto the track. WTOP's Hank Silverberg, who is on the scene, reports that four cars from the southbound train are on top of the northbound train, with the front of the cars completely split open. "It looks like a deck of cards falling on top of one another," Silverberg says. "It looks almost like the trains hit each other in a head-on collision." The trains look like "a tangled roller coaster," reports WTOP's Patricia Guadalupe, who is on the scene. Metro spokesperson Candace Smith calls the scene "terrible." "One rail car is about a third of the way on top of another rail car," Smith says. Metro officials are investigating the details of the derailment and collision, Metro spokesperson Cathy Asato says. The train was headed toward the Shady Grove station at the time of the accident, which occurred near the Maryland-D.C. border and the New Hampshire Avenue overpass. Metro trains typically run through the station around 44 miles per hour, Silverberg reports. All area hospitals have been advised to expect patients, Etter says. Metro is advising that people avoid the Red Line for the rest of the day. Trains are operating between the Glenmont and Silver Spring stations and between the Shady Grove and Rhode Island stations for the remainder of the day. Shuttle buses are operating between Silver Spring and Rhode Island Avenue Metrorail stations to help customers get around the incident. Metro buses can hold 50-60 people. MARC's Brunswick Line has been suspended indefinitely because of the derailment. MARC says it is trying to arrange a bus bridge. The derailment has not affected the Penn or Camden lines. (Copyright 2009 by WTOP and The Associated Press. All rights reserved.)