BLAZE: Brenda Bushell of the Papakura YMCA Early Learning Centre with part of the shelving burnt in the fire.

Teachers at an Auckland childcare centre are horrified that someone tried to set the building alight with 18 children and four staff inside.

One of the teachers at the YMCA centre in Papakura smelled smoke coming from the storeroom about 1.30pm last Tuesday.

When she went to investigate she found dolls and children's dress-up clothes alight on a shelf, centre manager Brenda Bushell said.

The flames were shooting up a wall so the teacher raised the alarm and began an evacuation.

She then tried to halt the spread of the flames with a fire extinguisher.

"Had she not done that the fire department said the room would have gone up and we wouldn't be open," Bushell said.

"It is just a scary thought that people would be that stupid to light a building on fire while children are inside."

Although the fire is the third at the centre in six months it was the first time someone had entered the building, Bushell said.

"The first two times were fires that were lit on the deck over the weekend."

Fire Service risk management officer Phil Faidley said he hoped there was no link between the fires but could not be certain.

"I can't say whether this signals an escalation or whether this is a completely separate incident. I would hope that this is a one-off and that we don't see this again.

"If somebody knows the person who did this they should get in touch so we get them the help they need."

Detective Senior Sergeant Aaron Proctor said that a fire set in a learning centre gave rise to serious concerns.

He's encouraging anyone with any information about the fire to contact him on 09 295 0244.