AFP/London

An attacker crept into a hotel room and hit three Emirati sisters holidaying in London so hard with a claw hammer that their skulls splintered, a court heard on Tuesday.

Philip Spence, 32, has admitted committing grievous bodily harm against the sisters at the four-star Cumberland Hotel in central London on April 6.

However he denies three charges of attempted murder and one of conspiracy to commit aggravated burglary and his trial on those counts began Tuesday at London's Southwark Crown Court.

Sisters Ohoud, Khulood and Fatima al-Najjar, from the United Arab Emirates, were sharing adjoining rooms in the hotel.

The "sustained and vicious" attack left all three unconscious, prosecutor Simon Mayo told jurors.

"Each woman was struck repeatedly to the head by a man wielding a claw hammer -- their skulls fracturing and splintering under the onslaught," he said.

"The intention of their attacker, say the prosecution, was to kill them.

"The scene that met the eyes of the police and emergency services as they arrived at the scene in the aftermath was, in the words, of one of those attending, 'horrific'."

The court heard the hotel rooms had been left open to allow a fourth sister to return later. Spence crept in and was seen by Khulood shortly before 1:30am, rifling through handbags.

She was in bed with her 11-year-old daughter and her sister Fatima, while her seven-year-old daughter slept on the floor.

"It is almost impossible to imagine the terror that must have seized these poor women as they were confronted in the darkness of their room by Philip Spence wielding that claw hammer," Mayo said.

"Worse still when he began to rain blows down on their heads."

The prosecutor said the "savagery" of the attack on Ohoud had been "even greater".

"Her skull was smashed so badly that brain tissue protruded from a hole in her head," he said.

Spence, from northwest London, fled with a suitcase full of valuables and it was not until the fourth sister came back that the scene was discovered.

The hammer was found outside the hotel.

Thomas Efremi, 57, from north London, also denies conspiracy to commit aggravated burglary.