2 December 2011 Last updated at 13:28 ET

Two hurt by concrete dropped from bridges over A12

Ch Insp Nick Morris said it was "pure luck" that no-one was killed

Two incidents where "bucket-sized" concrete blocks were dropped on to passing cars on the A12 in Essex are being treated as attempted murder.

A woman, 57, suffered life-threatening injuries when a block smashed the windscreen of a car passing under West Hanningfield bridge, on Thursday night.

Half an hour earlier, two women were left shaken after a block went through a windscreen at Fryerning Lane bridge.

Police are linking the attacks, which happened about eight miles apart.

The 57-year-old woman, from Harold Hill in Essex, was a passenger in a Nissan Ntec being driven by her 56-year-old husband, who suffered cuts.

The woman was cut out of the car by emergency services and taken to Broomfield Hospital, where she is said to be in a serious but stable condition.

The couple were returning home after visiting friends when their car was hit by the concrete block just after 22:00 GMT, Essex Police said.

'Despicable act'

A 26-year-old woman was driving a Vauxhall Astra which was struck under Fryerning Lane bridge at about 21:25 GMT.

The woman and her mother, 48, who were returning from a shopping trip in the Chelmsford area, were both unhurt but badly shaken.

Ch Insp Nick Morris said the concrete blocks looked as though they might have been moulded inside a bucket.

"It is attempted murder," he said. "If you throw a large piece of concrete off a road bridge on to a large, busy road, you are likely to kill someone.

"It's only by pure luck a lady was not killed last night."

Gary Sanderson, of the East of England Ambulance Service, said: "First and foremost this is a despicable act to carry out.

"We believe the concrete was thrown from a bridge across the carriageway when it collided with the car, entering the windscreen and hitting the woman."

Both bridges were cordoned off while forensic investigations were carried out.