Eleven worshippers were killed when they were dragged out to sea by strong waves at a beach ritual in Indonesia.

Twenty-three members of the Padepokan Tunggal Jati Nusantara spiritual group gathered at the Payangan Beach in Bondowoso Regency, East Java Province to perform a ceremony shortly after midnight on February 13. However, powerful waves dragged them out into the sea.

Adjunct Commissioner Muhammad Nai, head of the Jember Air and Water Police Unit, said: 'They arrived at the beach Saturday (February 12) midnight. Then, in the early hours of Sunday (February 13), they went down to the sea to carry out the ritual and were swept away by the waves.'

Residents around the beach had earlier told the group not to approach the water because of high waves, but the worshippers carried on despite the warnings.

Muhammad said: 'They were all swept away by the waves. Local residents then reported to SAR officers and assisted in the search.'

A total of 12 people were rescued during rescue operations which lasted until Sunday afternoon, while 11 people were reported drowned.

Officers said the group performed the ritual to 'calm themselves down,' and are now investigating if there is a criminal element involved in the incident.

Jember Police Chief Adjunct Senior Commissioner Hery Purnomo said: 'We will investigate further. We are waiting for the group leader's health condition to improve, so that the investigation can be continued. We will definitely examine him.'