Thick smoke trapped guests inside the budget hotel as firefighters rescued nine others and authorities began investigating the cause of the blaze.

At least nine people, including a child, have been killed in a fire that broke out at a hotel in Kolkata, India, according to the West Bengal Fire Services Department.

West Bengal Fire Services Director Anuj Sharma said thick smoke engulfed the budget hotel, with some of the victims found inside bathrooms.

The cause of the fire remains under investigation, although preliminary findings suggest that an air-conditioning unit may have exploded and triggered the blaze.

Firefighters rescued nine other people — six men, two women and a child — and took them to hospital for treatment.

Authorities were also working to establish the nationalities of those affected.

About 60 guests were reportedly inside the hotel when the fire broke out, raising concerns about safety measures at the building and the speed of the evacuation.

Hotel and building fires remain a recurring problem in India, where authorities have repeatedly raised concerns about inadequate firefighting equipment and poor compliance with safety regulations.