Pacific Gas & Electric is investigating the cause of what could be a gas leak that has blanketed a large portion of East Palo Alto and wafted over Palo Alto's Midtown area this evening.

As of 6:45 p.m., gas crews combing the area between University Avenue and Willow Road could not confirm the source of gas, or whether it was indeed a leak. Numerous teams are working with the Menlo Park Fire Protection District to track the source of the gas, said Fire Chief Harold Schapelhouman.

Schapelhouman said he smelled a strong odor all the way to Embarcadero Road and that the stench is slowly making its way through the west side of East Palo Alto. Schapelhouman said his department dispatched four engine crews to respond to several calls from East Palo Alto residents. The first call came in about 4 p.m.

About 6 p.m., the Palo Alto Fire Department began receiving calls about gas from residents in the Midtown neighborhood and later dispatched a crew to investigate the water treatment plant and landfill site off Embarcadero Road.