A 35-year-old man has been arrested in Motherwell, Port Elizabeth for allegedly murdering a grandmother and five children in Zwide, police said on Monday.

Police spokesperson Marinda Mills said Xolile Nelani was arrested on Wednesday by organised crime detectives.

She said Nelani appeared in the Port Elizabeth Magistrate's Court on Monday on six charges of murder.

Mills said the case had been remanded until 12 May and Nelani would remain in custody.

The grandmother and children were murdered last year in March.

The five children were allegedly drowned in a bath tub while the grandmother was hit with a blunt object.

Mills said no items were taken from he property and police were still investigating the matter.

She said Nelani was not related to the family.

The provincial commissioner of SAPS Eastern Cape Mpumelelo Landu said the case had been challenging but the persistence of the investigators had led to a breakthrough.

Sapa