Three Pakistan nationals died in a fire Friday in the northeastern Spanish city of Barcelona which left another four people injured, police said.

The fire broke out early Friday morning in the basement of a building in the Barceloneta district of the city, killing three men, "all Pakistani nationals", a police spokesman told AFP. 

Of the four injured, one was in serious condition, the mayor's office said. Police are looking into the cause of the fire incident that was occurred in La Barceloneta neighbourhood of the city.

Barcelona is the economic centre of the Catalonia region and is home to a large number of immigrants.

However, there are conflicting reports about the reason behind the deadly inferno. It is said the victims used to run cycle rickshaws and also charged the batteries at their house. It is feared that one of the batteries exploded, causing the fire which engulfed the entire house.

On the other hand, the local fire brigade says the incident may be caused by electric short circuit. The dead have identified as Sarfraz son of Saleem Khan, Mazhar Saleem son of Saleem Ahmed and Abu Sufiyan son of Tanveer Ahmed. They hailed from Jajokey village of Union Council Buddha Goraya located in Gujranwala district of Punjab. 

Meanwhile, the injured – Qamar Salim, Faisal Salim, Muhammad Qadeer and Imran Beg – are receiving treatment at a hospital.