West Yorkshire Police were called to reports of loose horses at New Road Side and Horsforth Ring Road at 4.15pm.
Bus services are delayed by up to an hour after the incident earlier this afternoon.
First Bus West Yorkshire tweeted: "Leeds area is encountering peak-time traffic congestion.
"Reports of an earlier incident on the Broadway Horsforth Ring Road which had severe traffic delays due to loose horses in the carriageway."
There is standstill traffic across Horsforth with delays extending to Abbey Road in Kirkstall and Horsforth Ring Road (A6120) towards Weetwood.
Delays are building up across West Leeds in Rodley, Farsley, Calverley and Bramley.