Children applying to six popular schools may need to go through balloting in the third of seven phases - Phase 2A2 - in the annual Primary 1 registration exercise.

Catholic High School, Nan Hua Primary, Nanyang Primary, Pei Hwa Presbyterian Primary, Red Swastika School and Rosyth School were oversubscribed when Phase 2A2 closed on Tuesday night.

Phase 2A2 is for children whose siblings or parents are alumni, whose parents are staff of the school, or who are currently in a Ministry of Education (MOE) kindergarten located in the primary school.

At this stage last year, 11 schools had more applicants than vacancies available.

Parents of children who need to face the ballot at this point will receive the results via text messages tomorrow, after computerised balloting is done centrally by MOE.

A total of 70 of the 185 schools in this year's exercise had filled more than half their places by Tuesday - down from 82 schools at the same stage last year.

In recent years, some schools have faced a squeeze because of a rule introduced in 2014 that requires all primary schools to set aside 40 places for children in the later stages: Phases 2B and 2C.

Phase 2B is the fourth phase in the exercise. It is for children whose parents are school volunteers, active community leaders or have ties to church or clan associations directly connected with the schools.

Registration for Phase 2B starts next Monday.

Phase 2C is considered the most competitive, as it sees the most number of schools needing a ballot, compared with earlier stages of the exercise. It is for children who have no ties to those primary schools.

Online registration for Phase 2C starts on July 29. Registration at the schools will start on July 30.