Three children died in a fire on Saturday at a building used by a private tutoring company as a childcare facility in the Changxing Island Economic Zone in Dalian, Liaoning province.

The blaze broke out as 24 sixth-grade primary school students were attending an English class.

One male student and two female students died at the scene and another student was slightly injured, the fire department responsible for the economic zone said on Sunday.

The zone's public security sub-bureau said on Monday four people had been detained in connection with the fire, including two owners of the tutoring company.

A teacher who was giving a lecture at the time helped to organize the students' evacuation. Firefighters found the three dead students in a bathroom on the second floor.

The fire department said it took 25 minutes to put out the flames, which engulfed 80 square meters of the two-floor residential building.

According to a preliminary investigation conducted by the police, the father of a man who rented the two floors had been frying chicken wings with an electric frying pan at his stationery store on the ground floor and had forgotten to switch off the pan when he left to look after his son's business.

After the man returned and found the pan had caught fire, he allegedly threw it to the ground and set the wooden floor on fire and the blaze spread to the second floor where the classroom was located.

The father and the two owners of the private tutoring company are being held on suspicion of being responsible for the three deaths, the police said.

The city's education bureau has set up a work group to probe the matter and the bureau head has visited the zone to assist with the investigation.

A woman surnamed Jia, who is the sister of a 12-year-old female victim, said the tutoring company collected students from schools each weekday at 4 pm and took them to the classroom to supervise them in finishing their homework until 6 pm. The center also provides tutoring classes on Saturday between 8 am and 4 pm, she said.

Jia said the cost of the service ran to 400 yuan ($61) per month.

Investigators believe the private tutoring company may have broken regulations prohibiting the setting up of a classroom in a residential building.

Childcare facilities and tutoring services are supposed to be registered and must meet certain standards but many consider the costs too high and unregulated providers of such services have become increasingly common.