Federal investigators are at the scene of a freight train derailment on a New Jersey bridge that forced hundreds of evacuations after four tanker cars tumbled part-way into a creek and spewed hazardous gas into the air.

Dozens of people were sickened and now train company officials, their contractors and environmental experts need to determine the best way to get thousands of remaining gallons of chemicals, now in a solid state, out of a damaged tanker.

The situation worsened Friday evening as readings showed higher levels of vinyl chloride in the air and authorities decided to evacuate several hundred people -- far more than immediately after the derailment.

The accident happened on a swing-style rail bridge where there was another derailment three years ago.

A crane is being floated in by barge from New York Harbor -- a full day's journey away -- to lift the tanker cars.