Police in Italy are searching for the body of an 18-year-old girl suspected to have been killed by her Pakistani family after refusing an arranged marriage.

The girl's parents, an uncle and two cousins are under investigation for murder, lieutenant colonel Stefano Bove of the Carabinieri police said on Saturday.

All “are supposed to have taken part in the crime”, he told reporters, while officers were combing through farmland to find the missing girl, Saman Abbas.

Bove said Carabinieri were inspecting “wells, irrigation canals and greenhouses”.

Saman Abbas, who lived in the northern town of Novellara, last year rebelled against her family's plan to have her wedded to a cousin in their home country.

While still a minor, she turned to social services and in November was moved into a shelter home. She also reported her parents to police, but on April 11 returned to them.

Police has been searching for her since May 5, when officers visited her house and found nobody, triggering an investigation.

Officers then discovered that the girl's parents had left for Pakistan without her, and found images from a nearby security camera that made them fear the worst.

Late on April 29, five people can be seen walking off from the house holding shovels, a crowbar and a bucket, and returning after about two-and-a-half hours.

The Carabinieri have identified the five as the family members suspected of murder. All are believed to have left Italy for Pakistan.

Meanwhile, hundreds of people took part in a solidarity rally for the missing girl organised on Friday night by the town hall of Novellara.

“Saman, tonight you are not alone and you will never again be alone,” Mayor Elena Carletti said in a video posted on local news website Reggioonline.