Open-air tour bus crashes in San Francisco injuring 19 people

A double-decker tourist bus crashed in San Francisco's Union Square on Friday, leaving 19 people injured.

The tour bus was travelling at high speed when it lost control and crashed into a cyclist, two pedestrians and a number of cars before smashing into scaffolding of a construction site.

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KTVU reports that the driver is in a critical condition. It is not known if he had a prior medical condition and authorities say he will be tested for drugs and alcohol.

San Francisco Fire Chief Joanne Hayes-White said: "The police department will investigate what those circumstances involved, whether it was mechanical failure, whether it was driver error. It's way too early to tell right now."

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According to the Press Association, the scaffolding was in front of what will be a new Apple store.

The bus also knocked down power lines use to propel San Francisco's fleet of electrical buses.

Around 30 people were believed to be on board when the vehicle crashed.

Three men and three women between the ages of 20 and 60 are in a critical condition.