An unexploded WWII bomb discovered near tracks leading to France's busiest train station has severely disrupted rail service as police work to disable the device.

All domestic and international trains at Gare du Nord, Europe's busiest train station, came to a halt Friday after an unexploded World War II shell was discovered, officials said.

The unearthing of a 500-kilogram World War II bomb near tracks outside Paris on Friday halted traffic and stranded thousands of passengers in one of the biggest rail disruptions in the French capital in years.