All schools, tertiary institutions and early childhood institutions in Christchurch, Selwyn and Waimakariri have been closed until further notice.
A shallow 6.3-magnitude quake struck at 12.51pm on Tuesday, 10km south-east of the central city, causing many deaths and widespread devastation.
The worst-hit institution is believed to be King's Education, an English-language school that occupied the third floor of the central-city CTV building that was destroyed in the earthquake.
Radio New Zealand understands a group of Japanese students were at the school at the time and some were unaccounted for on Wednesday.
The Japanese Consulate in Auckland says it's concerned for 24 people trapped in a building in Christchurch, though it's not clear if these are the King's Education students.
No other schools or tertiary institutions have reported serious injuries.
Christ's College says it suffered major damage and there is still a danger of falling masonry.