TOKYO — Whether Japan’s ruling coalition can retain its majority in the lower house remains unclear just days before the Sunday election, with Nikkei polling showing a close race in nearly half of single-seat electoral districts.

The Liberal ruling Democratic Party and coalition partner Komeito, which together held 279 of the 465 seats in the House of Representatives, look set to lose ground to the opposition. The largest of these parties, the Constitutional Democratic Party, is eyeing 150 seats, which would mark a sharp increase from its previous 98.