A schoolboy was hunted down by a "brutal and merciless" pack of 20 teenagers, who repeatedly stabbed him and left him dying on the floor of a station during rush-hour, a court heard. Sofyen Belamouadden, 15, was pursued through crowds of commuters at Victoria station in London by a gang from a rival school, who had planned ambush on Facebook.

"He was given no chance of life," Mark Heywood QC told the Old Bailey at the trial of eight of his alleged killers. "So brazen and confident were his killers that they openly carried the various weapons that they used with them as they ran towards him and together hunted him down.

"Such was their arrogance that they carried out that kind of attack in the heart of the capital city, in a public place, a terminus station at the height of the rush hour, and in sight of scores if not hundreds of people passing by."

They were so heavily armed, the prosecutor continued, that no one at the station on the afternoon in March last year dared challenge them as Sofyen was stabbed nine times, punched and kicked.

The teenagers, many of whom are so young that they cannot be publicly named, all face charges of murder, conspiracy to cause grievous bodily harm and violent disorder. Samuel Roberts, of Camberwell, Obi Nwokeh, of Bermondsey, Enoch Amoah, of Camberwell, and Victoria Osoteku, of Deptford, all 18, have pleaded not guilty to the charges along with four 17-year-olds.

Tensions were simmering between the two west London schools, with some pupils seeing the station as "home territory", and the attack was said to be revenge for an "inconsequential" skirmish the previous day when a boy had been left with a bloody nose, the jury was told.

During Facebook and mobile phone chats that evening, some of Sofyen's alleged killers talked about arming themselves with knives and a sword. One message said "they will get slumped" – meaning "killed or seriously harmed", explained Mr Heywood.

At lunchtime on the day of the attack, Miss Osoteku went out of school with one of the 17-year-olds to buy a block of five knives for £3.99 from Argos.

They then went to the station to confront Sofyen and his friends, who turned and fled "hopelessly outnumbered". Witnesses said they saw youths armed with weapons such as a samurai sword, flick knife, Swiss Army knife and possibly machetes and screwdrivers.

Sofyen was chased across the concourse, pushed down the stairs into a packed Underground station ticket hall where he lay helpless on the floor as he was stabbed, cut, kicked and punched during the "brief but ferocious attack".

"He was so wounded by then that any recovery was beyond reach. Despite expert medical attention given to him, he could not be saved," said Mr Heywood. "His life simply ebbed away. The level of aggression was indescribable," he added

The trial, which could not be reported until today because of previous reporting restrictions, continues.