The Catholic, Anglican and Methodist Churches are all participating in the vigil, asking God for unity between the city's different communities, and praying that demonstrations remain peaceful.
The English Defence League is protesting over concerns about the Islamic faith in the city and country.
At the same time a counter-demonstration is taking place, with multi-faith prayer, church choir singing, henna painting, street artists and local mosques providing free hot food.
Canon Timothy Lipscomb, vicar of Preston, is taking part in the vigil, and said the city has "exemplary" community relations, where faith leaders regularly work and socialise together and people of all faiths are "proud to be Prestonians".
The vicar also said local Muslim schools often come into his Church on trips to learn more about Christianity.
He told Premier: "We feel that actually it's only through prayer that we can find unity.
"If we're going to give a message of love and unity then we need to do something about it, and I think the only person who can really help is God.
"I think one of the most difficult things about looking at cultures and faiths is to generalise, because you can't really.
"Obviously in all faiths there are extremists and there are fundamentalists, and I'm wary of those people because they don't always listen to what other people say.
"But the more we try to understand each other and the more we try to find similarities rather than differences, the closer we will get.
"I know people are praying for me from other faiths, and I'm praying for them."
The English Defence League said on Facebook about today's protest: "Everyone travelling to Preston today, stay safe, stand proud and sing loud!!
"Have a great day and don't give way to usual provocation by leftards.
"PRESTON, WE'RE COMING!!!!"
Listen to Premier's Aaron James speaking to Canon Timothy Lipscomb:
