The victims were among a group of people barbecuing sausages and other food on Monday evening after the Böög burned in a bonfire at the Sechseläutenplatz on the shore of Lake Zurich, police said on Tuesday.
As people were grilling food shortly after 8pm an explosion came from the “still glowing pyre” where the snowman was lit, police said in a statement.
The victims near the remains of the bonfire needed medical treatment for injuries caused by flying debris, the statement said.
Two women, one man and the 11-year-old child were transported to hospital for checks, while five people reported suffering hearing damage.
According to the initial findings, police believe someone deliberately threw a fire cracker in the bonfire.
Further drama unfolded nearby, when a horse used in Sechseläuten ceremonies organized by Zurich guilds, collapsed and died of a heart attack.
The horse toppled onto its rider but he escaped serious injury, according to a report from the SDA news agency.
Members of the guilds — historically, groups of craftsmen who helped govern the city that have evolved into social clubs — parade in traditional costumes on horseback around the bonfire when the Böogg is burning.
The horse’s death prompted the Zurich association for the protection of animals to call for a ban on their use at the Sechseläuten event, SDA said.
According to custom, the sooner the Böögg, made of wadding, explodes, the better the summer will be.
This year it took 20 minutes and 39 seconds to burn, signalling rotten weather ahead.
On the bright side, predictions from past Böögg bonfires have been wrong every year for the past decade.