Police in Spain have seized more than 100kg of methamphetamine by chance in a Madrid shopping centre car park.

While investigating a separate incident at the car park yesterday, Spanish National Police officers observed a man acting oddly around a parked car.

Police said the person checked their mobile phone several times and picked up a vehicle key that had been left on a front wheel of the car.

As the man tried to leave the car, police officers stopped him and searched the vehicle.

Police said they found seven bags of building materials with 66 bags of methamphetamine hidden inside.

A man was arrested at the scene.