As a result two vintage Daimler cars worth an estimated £15,000 were destroyed and the fire was so intense children from Bamford Playgroup had to stay indoors for an hour to avoid the smoke.

No one was injured, but a female assistant in the filling station was sent home from work to recover. She was still too shaken to speak to the Observer at the time of going to press.

Detective Sergeant Graham Hook said: "Though no one was injured in this robbery, staff were badly shaken up and a substantial amount of cash was stolen.

"In order to ensure that we catch those responsible and that others are not subjected to a similar ordeal, we would appeal to anyone with information to contact us."

Fire crews from Rochdale and Heywood spent more than an hour tackling the blaze before bringing it under control.

Neil Fox, a watch commander, said: "It seems the Mercedes car has been involved in a robbery then it’s been dumped and deliberately set on fire. The fire has spread to the adjacent garage and then completely engulfed two limousines and a garage.  Fire crews from Rochdale and Heywood were at the scene for over an hour until the fire was extinguished."

The owner of the Daimlers, James Pointon, of Sapphire Wedding Cars, said: "As far as I know the car was burnt out then it spread to my garage.

"I received a call from someone close by explaining what had happened and when I found out I obviously wasn’t pleased at all.  I think there’s at least £10,000 to £15,000 of damage."

Catherine Bearshaw, from the nearby Bamford Playgroup, was relieved that the children were indoors when the attack happened. Staff from the nursery reported hearing several small explosions, but managed to keep the youngsters away from the fire.

She said: "We were getting the toys out when we noticed some smoke.  We didn’t see anyone running away from the scene because it happened so quickly. It looked quite serious but we kept the children away from what was happening."

All three suspects were wearing balaclavas and dark coloured clothing. They spoke with Manchester accents. The man carrying a machete was about 6ft 3in tall.

Anyone with information is urged to contact Rochdale CID on 0161 856 4591 or Crimestoppers anonymously on 0800 555 111.