From accounts they don’t appear to be ‘serious.’ BBC are reporting they may be detonators only and dummy bombs. A bus also has top deck windows blown out. No casualties, except possibly someone holding a rucksack that exploded.
Seems odd. Faulty bombs? Botched attempt to just cause panic.
Don’t dismiss these attempted, botched, copycat, etc. bombings out of hand.
The explosive is quite unpredictable if not made just exactly right.
Wait for the experts analysis.