A woman was forced to jump from a first floor flat window after a "severe" fire broke out in Preston overnight, say police.
The woman raised the alarm after she ran from her home on Aughton Walk near Lancaster Road and flagged down a passing police patrol.
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Four police officers, who were first on the scene, bravely entered smoke logged flats and forced entry to rescue residents as the fire raged in a neigbouring property.
The officers and the woman were all taken to hospital for smoke inhalation.
Firefighters from Preston, Penwortham and Bamber Bridge arrived to find a "severe" fire with flames leaping from the windows and thick black smoke pouring out of the properties.
Watch Manager David Shaw said: "We were called at around 3.30am on Thursday, to a persons reported fire in a ground floor flat.
"When we arrived we were met by a serious and well developed fire, which had spread to two flats above the property.
"Thankfully nobody was in the flats when we arrived, however, a lady who lived above the flat had to self rescue from a window of the flat.
"She jumped out of her window and and flagged down a passing police patrol.
"Police officers then swiftly evacuated flats around the property.
"The officers tried to get into the ground floor flat over fears that somebody may still have been in there but were beaten back by the severity of the fire.
"Thankfully, nobody was in the flat.
"In total 12 people were evacuated from the flats by the police, all of them were adults.
"Three flats have been left uninhabitable following the fire.
"At this stage we do not know if smoke alarms were fitted in these properties,but we would like to remind members of the public that it is absolutely critical that people have working smoke alarms fitted in their properties.
"The fire service will fit these free of charge."
Crews spent around an hour bringing the fire under control and remain at the scene today to begin investigation work into the cause.
The police officers have since been discharged from hospital. One woman remains in hospital as a precautionary measure.
A spokesman for Preston police said in a post to Twitter: "During the night we have responded to a substantial flat fire just outside our Police Station.
"Officers battled thick smoke forcing entry to numerous flats, rescuing a number of residents.
"A number of officers have been taken to hospital to be checked over as a precaution."
Police are treating the fire as suspicious and an investigation is underway.
A 41-year-old man from Preston has been arrested on suspicion of arson and is currently in custody.