TAMPICO, Ill. (CBS) — Federal authorities are investigating the deaths of two 14-year-old girls, who were electrocuted in a wet field while de-tasseling corn in northwestern Illinois Monday.

As WBBM Newsradio 780’s Mike Krauser reports, one of the farm workers says he heard Jade Garza and Hannah Kendall screaming, and he ran to help, but could do nothing without becoming a victim himself.

The 14-year-old girls, both from Sterling, Ill., we de-tasseling corn, when the Whiteside County Sheriff’s Department says they were electrocuted by a field irrigator near the village of Tampico.

LISTEN: Newsradio 780’s Mike Krauser reports

The witness, a 13-year-old boy from Rock Falls, says the field was like a pond. The boy, Tristen Dudley, said several others also tried to help the girls.

The girls were later pronounced dead at CGH Medical Center in Sterling.

Two others were seriously hurt.

In all, six workers were treated at area hospitals.

They were among dozens working for St. Louis-based Monsanto, which says nothing like this has happened before.

As a precaution, the company has shut down its de-tasseling operations in the Sterling-Rock Falls area for the time being, according to spokesman Mark Cavenaile.

Cavenaile said more than 1,000 people have been working for Monsanto this summer. They receive training and are told to walk around irrigation systems.

He said the accident has been reported to the Occupational Safety and Health Administration.

(TM and © Copyright 2011 CBS Radio Inc. and its relevant subsidiaries. CBS Radio and EYE Logo TM and Copyright 2011 CBS Broadcasting Inc. Used under license. All Rights Reserved. This material may not be published, broadcast, rewritten or redistributed. The Associated Press contributed to this report.)