The body of a 16-year-old girl discovered in an alleyway bore signs of an attempt to set it on fire, police said.
College student Sasha Marsden was found dead in the South Shore area of Blackpool at about 9pm on Thursday. Police said a post-mortem examination will take place later.
A man and a woman are being questioned over the death of Sasha, who lived with her parents in the Staining area of the town and attended Blackpool and The Fylde College.
Specialist crime scene investigators are carrying out forensic searches of the alley behind Kirby Road and at a bed-and-breakfast hotel in the same road, which is a few blocks off the Promenade. Officers are also checking local CCTV cameras and carrying out house-to-house inquiries.
The two people arrested, a 22-year-old man and a 20-year-old woman, both from Blackpool, were detained close to the scene in Kirby Road shortly after the body was discovered.
Senior investigating officer Detective Superintendent Andy Murphy said: "This is an incredibly difficult and complex inquiry and we are working to try and build up a picture of what happened last night.
From examining the body, it appears to us that someone has attempted to set fire to Sasha, and this is a line of inquiry that we are looking into. This is an incredibly difficult time for the family, and we are keeping them informed of our investigation. Our officers will be supporting them as they attempt to come to terms with what has happened."
Blackpool police operations manager Superintendent Eddie Newton said: "Incidents like this do send a sense of shock throughout our communities, and I would like to reassure the Blackpool public that we have a team of dedicated and highly trained officers working on this investigation to try and establish exactly what has happened.
"I would ask people not to worry. We believe that this is an isolated incident and that there is no risk to the public. We have two people in custody helping with the investigation and detectives are following a number of different lines of inquiry."
Mandy Pritchard, head of school for society, health and childhood at Blackpool and The Fylde College, said: "Sasha was studying a level 1 childcare course with Blackpool and The Fylde College. Since enrolling with us last September, she had been making fantastic progress. Sasha worked hard and was looking forward to carrying out a work placement and progressing to level 2 and ultimately a career in childcare. She was a friendly, considerate individual who cared about her fellow students. Her classmates are understandably upset and the college is offering all the support it can at this difficult time. Our thoughts are with Sasha's family."