CHICAGO (AP) _ A water-main break in Chicago's Loop forced authorities to reroute elevated trains and close nearby streets Monday.

The break about 8 a.m. dropped water pressure in surrounding buildings, flooded streets and left several inches of water in some garages and basements. City engineers sealed four nearby water mains to stop the gushing water an hour later.

The break weakened the pavement and opened a sink hole 20 feet wide and 6 feet deep.

Water Commissioner Richard Rice said any number of factors, including frost and construction, could have caused the break. He couldn't estimate how long repairs would take.

The Chicago Transit Authority said initial tests showed no damage to the elevated rail station that sits just above the main break. But trains will be rerouted at least through Tuesday because of fears the rail structure may have been weakened.

``Have no illusions,'' CTA President Frank Kruesi said. ``It's going to be a long commute.''