Children as young as 11 may be trapped inside a school bus after it crashed on a main road in South Carolina.

The bus, carrying pupils from Pine Ridge Middle School in Lexington County, rolled over on Thursday afternoon after a tyre blew on I-77 in Chester County.

As many as 35 students were on the bus, as well as two adults, Fox 57 reported.

Local media reported 18 people had been hospitalised.