Fire officials are alerting motorists that they may see smoke and hear blaring sirens coming from the Webster and Posey Tubes between Oakland and Alameda late today and early Thursday, as firefighters conducting training drills.

The Webster Tube, which carries traffic from Oakland to Alameda, will close at 10 p.m. Wednesday and reopen three hours later at 1 a.m. Thursday. The Posey Tube, which carries one-way Oakland-bound traffic, will close at 1:30 a.m. Thursday and reopen 3½ hours later at 5 a.m. the same day.

The Oakland and Alameda fire departments are conducting drills in the tunnels connecting the cities of Oakland and Alameda to test equipment, practice working in the tubes and ensure the agencies can respond effectively in case of fire.

The fire departments say that one of the tubes will always be open, and that the closures are during nighttime only. Signs will be in place to help drivers, and the California Highway Patrol will be at the site.

Drivers from Oakland will detour south along Interstate 880 and cross the Oakland Estuary via the Park Street Bridge, while drivers from Alameda will detour east to Atlantic Avenue and cross the estuary at the Park Street Bridge.