ST. LOUIS (AP) — The lights — and perhaps more importantly, the air conditioning — are back on in downtown St. Louis after an underground fire knocked out electricity for much of the city’s urban center.

Crews for Ameren Missouri restored power Thursday afternoon, but not before several offices and business closed for the day. City Hall and the Carnahan courts building were among the buildings shut down.

Extreme hot temperatures and aging infrastructure were believed to be culprits for a fire inside a manhole that caused the outage at about 8:30 p.m. Wednesday.

The temperature was 98 degrees by mid-afternoon Thursday, with a heat index topping 100 degrees for the fifth straight day.

The outage affected about 2,100 customers, including many high-rise buildings. Ameren said power has been restored to most customers.