At least 20 people have been killed and others injured in a stampede during an outdoor religious service in Tanzania.

Worshippers were attending a Pentecostal service at a stadium in the northern town of Moshi on Saturday evening when the incident occurred.

Moshi district commissioner Kippi Warioba said attendees rushed forward to be anointed with blessed oil.

Tanzania's President John Magufuli sent his condolences and called for better security at such large events.

The service was held by pastor Boniface Mwamposa, who refers to himself as "the apostle".

Survivors said Mr Mwamposa told hundreds of people gathered at the service to pass through an area where "blessed oil" had been poured over the floor.

The crowd rushed forward to try to step in the oil in the hope of being cured of sickness.

Peter Kilewo, who attended the service, described the scene as "horrible", telling AFP news agency that people were "trampled on mercilessly, jostling each other with elbows".

He added: "It was like the preacher had thrown bundles of dollars about."

Police said Mr Mwamposa was being held for questioning.

Mr Warioba said the authorities were looking into whether more casualties were taken to other local clinics, health facilities and hospitals.

"The incident took place at night and there were many people, so there is a possibility that more casualties could emerge. We are assessing the situation," he told Reuters.