BATON ROUGE, La. (AP) _ A chemical spill from a grounded barge on the swollen Mississippi River put this city on alert Tuesday and forced the evacuation of hundreds of people on both sides of the river.

The stranded barge was one of a string of 25 that struck the U.S. 190 bridge over the Mississippi and broke free Monday. It was carrying 400,000 gallons of the chemicals toluene and benzene, both flammable and toxic.

The barge overturned near the west bank and began leaking below the water line. More than a dozen families were evacuated in Port Allen, and on the east side in Baton Rouge, Southern University was evacuated as well.

State police spokesman Capt. Ronnie Jones said instruments showed benzene in the air. ``You can clearly smell the chemical,'' he said.

The concentration of fumes was in the safe range although shifting winds made the measurements difficult.

Automobile traffic on the U.S. 190 bridge and the nearby Interstate 10 bridge was closed after the accident.

``Right smack dab in the middle of rush hour, we shut down both bridges,'' Jones said.

Southern University, about two miles away, closed down as a precaution. Half of the 2,600 students who live on campus went across town to spend the night at Louisiana State University's cavernous fieldhouse. Most of the others moved in with off-campus friends, local students and their families.

Many students were annoyed that the school waited hours to announce the evacuation, especially since spring break starts Friday.

``This is just ridiculous. I was hoping to go home before Friday anyway. I wish I could have left this morning,'' said Sabiaa Alexander, a freshman from Seattle, Wash.

``All I brought to this place was a change of clothes,'' she said. ``I don't have a blanket or a pillow. Nobody told me to bring anything like that.''

Baton Rouge's business section, including the Capitol, was under alert. The gambling boat Casino Rouge shut down voluntarily at dusk and The Advocate newspaper pushed up its deadline in case the evacuation zone was expanded.

The Mississippi is swollen with floodwaters from the Ohio River and the U.S. Army Corps of Engineers began diverting some of the water Monday.

A 2 1/2-mile stretch of the river was closed and a swift current played havoc with barges on the river.

As teams worked on the leaking barge, another batch of 12 broke free about six miles downstream, but they were quickly brought under control.

Divers went into the fast-moving river during the night in an attempt to stabilize the barge and a crane was being shipped from New Orleans to lift the barge from the river and remove its toxic cargo, Jones said.