A four-year-old girl was beheaded in Taiwan in what appears to have been a random knife attack, state media said. 

On Monday morning, a 33-year-old man attacked the girl with a cleaver in full view of her mother as they were on their way to a metro station in Taipei, the island's capital, the official Central News Agency (CNA) said.

The mother of the slain child said her daughter had been riding her bike about a meter away from her when it became stuck.

She saw the man approaching and at first thought he was going to help her daughter but he drew his knife and decapitated her.

"I saw the suspect slashing my daughter with a cleaver. I immediately grabbed him but I could not pull him away," she said.

Bystanders heard her screams for help and rushed to restrain the attacker until police arrived.

An initial investigation found that the suspect, identified only by his surname Wang, waited near the metro station after allegedly purchasing the knife at a supermarket earlier that day.

Citing police, CNA said the man had a history of mental illness and had received treatment at a psychiatric hospital.

The suspect was detained at a police station, where a large angry crowd gathered. Officers attempted to escort him out of the building, still with blood splashed across his face, but several people rushed the suspect, eventually forcing police to take him back inside.

Read: Man stabs passengers aboard Taiwan train

In 2014, a 21-year-old Taiwanese man Cheng Chieh went on a mass stabbing spree on the Taipei metro system, killing four people and injuring 24 more.

(CNN)