Detectives were today hunting firebombers who attacked a primary school.

A mobile classroom was destroyed at Windhill C of E Primary School, Shipley, in what fire investigators said was a deliberate attempt to cause maximum damage.

It was the second arson attack at the school in a matter of weeks.

And on Sunday, firebugs attacked the former Low Ash Primary School in Oakdale Avenue, Wrose, less than a mile away.

Police today said they did not know if the attacks were linked.

Shipley firefighters were called to the school in Wrose Brow Road after a loud explosion was heard from the mobile classroom.

The school's chairman of governors, Councillor Mark Blackburn (Lab, Shipley East), said: "This is the second attack on the school and it is very worrying for us all.

"The culprits must be caught before any further attacks cause even more damage and lives are endangered."

Head teacher Caroline Illingworth said the staff and pupils were devastated as the blaze had also destroyed pupils' work.

"It is very distressing for all of us," she said. "Work done by Year Five and Six pupils has been destroyed and those pupils will not be in school this week as there is nowhere for them to be taught.

"A stone was put through a window and then a petrol bomb thrown in afterwards. The classroom ceiling has melted and there was no electricity in two rooms."

Sub officer Chris Clarke, West Yorkshire Fire Service's fire investigation dog handler who surveyed the site, said the attack had clearly been planned.

"It was a very serious incident and there appears to be a real intent to cause a lot of harm," he said.

"It has gone beyond just youngsters playing a prank. We are still investigating but petrol was clearly used and there was a trail of petrol found across the school playing field."

He added that fire officers would be going into school next week to talk to youngsters about fire dangers.

"There was an incident in mid- December at the school where petrol was used to start a fire in the porch of the school but there was no serious damage caused that time.

"This is altogether a more serious and deliberate act and we are determined to carry on our investigation into the cause of the fire and assist the police as much as we can to catch the culprits."

Last week Bradford councillors agreed to spend £500,000 on a fire safety programme for its schools during the next financial year. It involves upgrading alarm systems and emergency lighting and an increase in security.

In 2002 there were 41 fires at schools in the Bradford district, 32 of them deliberate. The previous year 55 out of 67 blazes were treated as arson.

Councillor David Ward, Bradford Council's executive member for education, said the Windhill fire was a clear case of arson.

"Unfortunately there are criminally idiotic people around who are capable of such acts. There are 200 schools in Bradford and we have to be vigilant all the time in terms of security."

He added: "I am sure the school had all the proper procedures in place. Mobile classrooms are just more vulnerable because they are set apart from the school."

A police spokesman appealed for information about those responsible for the attack which took place at 8.15pm on Tuesday.

"Such wanton vandalism will not be tolerated by the police," he said.

"The actions of those responsible affects not just the children but the whole community."

Police should be contacted on (01274) 376059. Our picture shows Windhill teacher Joan Fletcher in the damaged classroom.