Four masked man have escaped with a large amount of cash after holding up a security van outside an Oxford bank.

The gang - who were armed with handguns - ambushed a security guard as he arrived at the Abbey bank in Banbury Road, Summertown, at 5.30am today, and escaped with a substantial amount of money.

The guard, who works for G4S, also known as Group 4 Securicor, was injured in the attack and has been taken to hospital. His injuries are not thought to be serious.

The raid follows a similar attack on the Abbey bank in Abingdon precinct just over two weeks ago but there has been no formal linking of the robberies.

Detectives cordoned off the shopping parade in Summertown this morning and are speaking to witnesses.

Acting Det Insp Kevin Elkins, of Oxford Police, who is leading the investigation, said: "We believe the offenders made off in a white Corsa van towards Woodstock Road, and I appeal for anyone who saw that vehicle or anything else suspicious around that time to contact me immediately.

"The men were armed with what is believed to be handguns but no shots were fired."

Shortly before 9am, staff from the Abbey arrived to get into the branch but were forced to wait outside while police continued their investigation.

Officers have removed a blue Vauxhall Corsa and a silver Mercedes from the scene.

A spokesman for the Abbey bank said no further details were being released at this stage.

One of the four robbers is black while the other three are white but there are no detailed descriptions of their appearance.

Anyone with information is asked to telephone police on 08458 505505.