I think the station (two transfer stations, actually) where it occurred is a pretty busy one for St Petersburg commuters. I was there in the fall and I was actually impressed by their metro lines - and, of course, Moscow’s metro is super impressive and quite old.
I read that 12 people are dead now. They found two dead in the tunnel.
I used to commute between Primorskaya, Mayakovskaya and Politechnicheskaya.
Prayers up.