An articulated lorry and a U4 bus were in collision in Oxford Road, Uxbridge, at the Mahjacks Roundabout, today (Thursday) at about 4pm.
Traffic chaos is likely as the rush hour draws on.
The lorry's cab was left sticking out into the roundabout lanes, its Maersk shipping container trailer wedged against the bus. The two vehicles were blocking one lane of the southbound Oxford Road just as it joins the roundabout.
Passengers on the bus described a loud "scraping" noise.
Murial Neasby, 81, of Hayes told the Gazette: "It was very loud and took us all by surprise.
"Nobody was hurt thankfully.
"We were sat on the bus waiting for the police to come but after 10 minutes the driver had to let us off as it was getting too hot.
"I don't know why it took [the police] so long to get here."
Police officers were directing traffic at about 5pm.
