UPDATE:  Brookfield Zoo planned to be open for business as usual Saturday following Friday’s gas main break.

CHICAGO (CBS) — The main entrance at Brookfield Zoo had to be closed Friday after a gas main break nearby, and its smaller south parking lot quickly filled to capacity.

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Brookfield Zoo spokeswoman Sondra Katzen said a 3-inch gas pipe ruptured near its north entrance at 31st Street and Golf View Road around 11 a.m.

It was not immediately clear how the gas main ruptured, but construction crews were working in the area at the time.

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The north parking lot was closed while crews worked to repair the broken gas main, and the south lot quickly filled to capacity, so no other vehicles were being allowed in the south entrance, though the zoo itself was still open. The main lot on the north side of the zoo holds approximately 3,500 cars, while the south lot holds only 520.

Another 420 cars can park at the lot at the zoo’s Discovery Center, which is accessible only through the south entrance.

The zoo was making accommodations for visitors who parked in the north lot and cannot get out. Officials estimated the north lot would be closed until approximately 2:30 p.m.

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Meantime, all visitors must enter through the south gate, along Golf Road, near Riverside-Brookfield High School.