The four masked men were at large last night after a three-hour chase across Berkshire, which left a policeman injured.
On two occasions the gang, which held up a post office in Reading, opened fire on police, injuring Inspector Paul Kirby, of Thames Valley police.
They also brandished sawn-off shotguns at four motorists, and left a trail of battered vehicles.
At one stage they took a lorry as armed officers and a helicopter closed in. Police used tracker dogs, Land Rovers and a fleet of marked and unmarked cars as they kept the gunmen in sight.
'These men were totally ruthless,' a police spokesman said. 'If a police officer had confronted them, they would have shot him.'
A large operation was under way between Reading and Wokingham last night after the gang escaped in a hijacked car.
The gang used at least seven cars. Their initial getaway car, a red Montego, was stolen from Newbury, Berkshire.
Donna Cooper, 13, was killed yesterday in Rushall, West Midlands, when she was struck by a speeding, stolen car and then dragged 150 yards (137m).Reuse content