A three-year-old boy died on a London train platform on Wednesday night after suffering a suspected sudden cardiac arrest.

Onlookers at London Bridge station rushed to help the child after hearing ”screams of pain” from the child’s parents shortly after 9pm.

Commuters tried to perform CPR on the toddler before paramedics arrived at the scene and attempted to resuscitate the child for 20 minutes. He was then taken to St Thomas’ Hospital, where he died shortly before 10pm, the London Evening Standard reported.

“We were called to London Bridge station at about 9.12pm following reports of a child having collapsed," a British Transport Police spokesman said. "He was taken to St Thomas’ Hospital but he sadly died."

PR manager Melanie, who was standing on the opposite platform at the time, said: “I could hear screams of real pain, harrowing. I wondered if someone was in labour it was so intense. I was looking at the people on the stationary train. Everyone who was there was facing the scene. I don’t think anyone knew what to do or what was going on.

“The tannoy asked for any nurse or doctor to go to platform 5. The train in front never moved so I didn’t see anything. But those screams will haunt me.”

A London Ambulance Service spokeswoman confirmed that CPR was attempted by commuters on the child before he was taken to St Thomas's Hospital as a priority case.

She added: “We were called just before 9.15pm to reports of child in cardiac arrest at London Bridge train station. We sent an ambulance crew, a paramedic on a motorbike, an advanced paramedic and a duty manager to the scene. The first of our medics arrived within three minutes of the call coming into our control room."

Police said there were no suspicious circumstances regarding the death.