It's only a test, but all the sirens, flashing lights and scores of police and fire personnel scurrying around downtown St. Paul Wednesday morning will make it look like a real emergency.

Wall Street between Kellogg Blvd. and 4th Streets will be blocked off from 8 to 11 a.m. as the City of St. Paul and Xcel Energy participate in an exercise simulating an accidental break of a natural gas main resulting in the simulated release of natural gas into area sewers and buildings.

Citizens in the immediate area near the St. Paul Farmers Market and Union Depot are asked not to call 911. This will help 911 operators remain available to handle actual emergencies, a spokesman for Xcel Energy said.

For commuters on Kellogg Blvd., be aware that the intersection of Kellogg and Jackson Street is closed for the next 10 weeks for utility work. On Tuesday, that closure led to traffic snarls during the morning rush hour.