CORONADO (NEWS 8/CNS) - A possible transformer explosion caused traffic delays and other problems in Coronado Wednesday.

Most street closures were lifted before noon after trouble with the transformer outside a supermarket near Naval Air Station North Island.

Witnesses reported hearing an explosion, likely from the overloaded transformer, in an alley behind the Vons store in the 800 block of Orange Avenue in Coronado about 8:15 a.m., city spokeswoman Janine Zuniga said. The building then began to fill with smoke, and its fire-sprinkler system activated.

Emergency crews and store employees cleared everyone out of the building while firefighters extinguished the blaze, which caused no injuries. San Diego Gas & Electric personnel turned off the power supply to the building and were investigating the mishap.

"Right now, we aren't sure if the transformer or (a) refrigeration unit caused the fire," Coronado Fire Chief Jim Lydon said in the late morning.

The store was expected to remain indefinitely closed due to heavy smoke and water damage, and lack of electrical service. County health officials will assess the site before it is allowed to reopen to the public, Lydon said.