BAKU, Azerbaijan (AP) — The subway in Azerbaijan's capital has suspended service in the wake of a massive blackout in the Caspian Sea nation.

The authorities said the Baku subway will be closed for the entire day Wednesday due to unstable power supply. City officials provided extra buses to help commuters.

The power outage hit the ex-Soviet nation early Tuesday when a transformer at one of the nation's power plants caught fire. It was the worst blackout in Azerbaijan since the 1991 Soviet collapse, and energy workers were struggling for a second day to restore supply.

President Ilham Aliyev has set up a government commission to investigate the reasons behind the blackout.