The critter was discovered after hopping out of the Cairns woman's bag when she stopped by Ultimate Hikes shop ahead of the walk on the Milford Track, the Southland Times reported.
General manager Noel Saxon said staff caught the toad and contacted the Ministry of Agriculture and Forestry (MAF) who told them to kill it -- which was done by putting it in a freezer.
A MAF spokeswoman told the newspaper the woman had arrived from Sydney and declared her boots, which were then cleaned at the airport, but socks stuffed in the tops may have concealed the toad.
"We've tipped the boots, looked at them, cleaned them and returned them to the passenger."
While the toad had managed to infiltrate the country, had it escaped into the wild it would likely have perished in the South Island climate, the spokeswoman said.
