With the UK set to leave the EU on March 29, 2019, a trade deal has yet to be agreed by the two parties.
Speaking to 5 News on Wednesday, Mrs May said the UK is preparing for “every eventuality”.
She said: “Far from being worried about preparations that we’re making, I would say that people should take reassurance and comfort.
“It’s right that we say because we don’t know what the outcome is going to be [from Brexit negotiations], we think it’s going to be a good one.
“We’re working for a good one but let’s prepare for every eventuality.”
And on Tuesday new Brexit Secretary Dominic Raab confirmed the government would ensure that food supplies were adequate if no deal is reached.
Brexit campaigners have accused the government of using warnings over a no-deal Brexit to scare people into supporting Mrs May’s plans.
It comes as Mr Raab is in Brussels to meet the European Union’s chief negotiator Michel Barnier.
The Brexit Secretary has said he will bring “as much energy as I can” to the talks.