Oh yikes, folks. According to our increasingly favorite Twitter account to follow, Emergency_In_SF, they've got word (via timmysanfran) that there's a fire, possibly caused by an explosion, at Market (near Fourth Street) next to the massive Ross store.

Check it:

"Emergency_In_SF: @timmysanfran is reporting "fire at the Ross on 4th and market. 4th street is filled with smoke down to mission."

More info as it comes in to us.

Update 10:35: SFist commenter kindle writes, "Looks like people have gone back into the building but billows of smoke are still coming out from the 4th street side. It smells pretty awful!" Sounds like another manhole explosion, right?

Update 10:43: According to ActionNewsSF, "@apparentlymatt says no 30 or 45 [Muni bus lines] south of Market." Traffic is also shutdown at the Market and Fourth street area too.

Update 10:50: KRON 4 confirms it as an "underground fire," going on to say that Fourth Street (near Market) is closed.

Update 10:56: PG&E crews are on the scene and the fire is out. This most recent underground explosion comes on the heels of the Tenderloin vault fire, which happened last month. It sounds like, once again, PG&E has some explaining to do.

Update 1:02: SFist commenter FYoCouch247 says that "[r]eports have it where there is no power within a few blocks of the smoke, DPT has shut down the streets between 4th and 5th. MUNI has a bus bridge for their...bus lines. PG&E trucks are flooding into the
area and the SFFD PIO is on the scene."