It happened at about 08:25 on the A737 at Lauchlan Way, near Ayrshire College.
The Scottish Ambulance Service said one person had been freed after being trapped in a vehicle. No-one on the bus was thought to have been injured.
The college has tweeted that there may be some disruption to classes this morning due to a "major traffic incident".
Two ambulances and a special incident support vehicle were sent to the scene, the ambulance service said.

Screenshots posted by a computer science student in the US appear to show cash transfers between users could be coming to Facebook.
Earlier this year the social network's founder Mark Zuckerberg said that "over time" there would be some "overlap" between messenger and payments.
But Facebook declined to comment.
Andrew Aude, 21, posted screenshots of the payment function on Twitter.
He reportedly uncovered the facility using software which allows developers to explore and modify apps.
He added debit card details which apparently unlocked a way of sending money, just as you would a photo or emoji.
Speaking to investors in July, Zuckerberg warned that the company had "a lot of work to do" before offering a payments service.
"We're going to take time to do this in the way that we think that's going to be right over multiple years."
Earlier this year, Facebook hired former PayPal president David Marcus.
Several person-to-person payment apps already exist including Ribbon, Square Cash and Venmo.
So far these services have struggled to attract users in large numbers, particularly outside the US.
Facebook has 1.3 billion active monthly users, giving it the potential to become widely used as a payment service.
The social network has faced criticism for forcing users to use a separate app to send messages rather than the main Facebook app.
Adding mobile payments may help Facebook encourage people to use the messenger app more widely.
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Two people have been injured after a crash involving a car and a bus in Kilwinning in North Ayrshire.
[NEXT_CONCEPT]
Soon it may not just be smiley faces, big cats and a thumbs-up that you can send your friends on Facebook messenger.