Dramatic pictures show overturned lorry on major West Yorkshire rush hour route
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The A650 Wakefield Road at Dudley Hill, Bradford, has been closed in both directions, police said.
Traffic is building in the area according to the AA.
Buses including the 620, 617 and 618 are being diverted.
One twitter user described the traffic in the area as "absolute carnage", with long delays.
First West Yorks said: "Due to a RTC on Dudley Hill Roundabout - 620/617/618 services towards Holmewood will divert via Bowling Back Lane and Sticker Lane. 617 service will not be able to operate normal route to Bradford and will only be able to operate as 618 at present."
In a later update, First said: "Knock on effect of traffic,starting to affect surrounding areas. Expect disruption and possible cancelllations to some journeys across the network.