An air ambulance transported the woman, believed to be in her 30s, to the John Radcliffe Hospital in Oxford having suffered severe pelvic injuries.
The incident took place at about 1.15pm on the northbound carriageway of King Street near Grenfell Island.
It brought gridlock to Maidenhead town centre as emergency services rushed to remove the women from the one-way road where she had been knocked down by the lorry.
Traffic heading north along King Street towards the town centre was diverted along Shoppenhangers Road.
The road was not reopened until about 4.30pm.
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Police officers can be seen at Ten Pin Bowling in Maidenhead tonight following an incident earlier today.