About six to seven unidentified men allegedly cut the hair of a 60-year-old Sikh man and also threw acid on him in Bhogal area of south-east Delhi, the police said on Tuesday.
After the incident, hundreds of Sikhs staged a protest, demanding the arrest of the accused.
The incident took place around 7.30 pm on Monday when Ranjeet Singh Thapar, who plies an autorickshaw, was returning home.
His daughter Priya said, "Six to seven unidentified persons stopped him near a private hospital here and started thrashing him. Some minutes later, they cut his hair and then threw acid on his body."
"We don't know who attacked my father, he has no enmity with anyone," she added.
Thapar suffered burn injuries on his chest, stomach and private parts. He was hospitalised. His condition is said to be critical.
"The police have arrested one Soman Nayak and a case has been registered. CCTV footage is being scanning to identify the accused," said a senior police officer.
The officer said teams had been formed to crack the case.
Residents of Bhogal, a Sikh-dominated area, staged a protest on Tuesday and demanded immediate arrest of all culprits.
Traders of the Bhogal market shut shops to show their anger over the incident.
Security has been beefed up in and around the area to avoid any untoward incident.