Three police officers are under investigation after they were filmed striking a man and pinning him down while he appeared to be having a seizure during a traffic stop.

The incident took place at about 5.30pm on a residential street in Poplar, east London, when police told the man of Moroccan origin to move his car, which had a blue badge, from a single yellow line.

In video filmed by onlookers as officers wrestle him to the ground, one appears to be kneeing him and another can then be clearly seen hitting him three times with a pair of handcuffs on his torso and upper leg/hip. By the time the officers release him, he appears to be unconscious.

In a document sent to local community leaders amid widespread concern about the tactics deployed by the officers, police admitted to “holding him [in] place” while it appears “he is having a fit”. They said footage from officers’ body-worn cameras showed the man “lashes out his arm and appears to attempt to bite the arresting officer”.

Nevertheless, the incident has been referred to the central east command professional standards unit, but community leaders have said that given its seriousness it should be handled by the Independent Office of Police Conduct (IOPC).

In a video apparently filmed by the man, the police give him a “five-stage warning” (five chances) to move his vehicle or produce his driving licence. It ends when the officer attempts to handcuff him and the man says: “Don’t touch me.” Later footage shows the man repeatedly shouting: “I can’t breathe,” and “my heart” as the officers hold him down on the pavement.

At one point, an officer appears to drag a pair of handcuffs across the man’s head, causing it to bleed. The man then begins having spasms as officers continue to restrain him, while his wife, who addresses him as “Youness”, screams at them: “You’re killing him.”

As other officers arrive and try to push back members of the public watching and recording the incident, the officers holding him release their grip and he is shown unconscious, lying spreadeagled on the pavement.

His sister Amal Bentahar, 35, who lives nearby, said she was alerted to the incident when her sister-in-law called her. “When I went there I saw my brother with oxygen lying on the floor. It was awful. I feel very, very upset. Even the people who were watching around her feel this was too much. It’s like he’s a terrorist. It’s heartbreaking.”

She said her brother was visiting her with his wife and two children, aged four and two, who were in the car watching and crying. She said the younger child requires oxygen for a medical condition, which is why the car has a blue badge. Her brother was carrying flowers for her, which he dropped after being tackled by officers.

Bentahar said her brother was still feeling unwell and nauseous on Wednesday afternoon. Almost 24 hours later his car remained parked in the same place where police said it was obstructing the highway, with the blue badge displayed.

Salman Khan, 19, a sports teacher from west London, was a passenger in a car passing through the area when he stopped after seeing a commotion on the ground. “My heart was beating fast, I genuinely thought he was going to die,” he said. “They held his legs and arms and stopped him from moving but he wasn’t really moving, he was just shaking from the seizure.

“He’s having a fit, they should have let him go, tilted him to the side in the recovery position. It’s quite clear that even his legs are shaking and people are screaming: ‘Let go.’ They treated him [medically] too late and they were to blame for the situation.”

Residents seemed incredulous that an argument over a man parked in a spot they said was often used by other vehicles, including from the minicab firm a few metres away, could escalate so dramatically. Joynal Hussain, 26, said: “They grabbed his hands and started wrestling with him. They were hitting him. It was very upsetting. You’ve got the lady screaming, the children crying. It was emotional for everyone.”

Councillors, who have called a meeting for Friday to address residents’ concerns, said tensions with police were already high in the area.

John Biggs, the Labour mayor of Tower Hamlets, described the video as disturbing and said he had told the police they should refer it to the IOPC. “While we should avoid jumping to conclusions, everyone must be able to feel safe on our streets and have confidence in our police,” he said.

Jack Gilbert, the chair of the local safer neighbourhood group, also said the case should be referred to the IOPC, questioning whether it was “a proportionate response”.

Mark McEwan, the Met commander responsible for professionalism, said he understood how the incident looked to onlookers or people who had viewed footage on social media but that the man had resisted arrest, adding: “The man is subsequently arrested on suspicion of obstruction of the highway, assaulting police and resisting arrest. During the incident he became unwell – officers immediately assisted and called an ambulance. The man was taken to hospital for treatment as a precaution, and is now in custody at an east London police station. Two officers suffered minor injuries.”

• This article was amended on 12 July 2019. An earlier version misspelled Amal Bentahar’s last name and stated that Youness Bentahar requires oxygen for a medical condition when it is actually for his child.