Japanese Prime Minister Shinzo Abe has once again denied he misused his influence to help a friend in a growing favouritism scandal.

With support ratings for his scandal-laden cabinet hitting new lows, Abe was again questioned in the upper house of the Japanese parliament on Tuesday over allegations he intervened to help his friend gain approval to open a new veterinary school in western Japan.

Abe told the legislators he was not asked by his friend for help in gaining approval for the opening of the school in the city of Imabari, on the southwestern island of Shikoku.

On Monday, Abe denied the allegation at a similar session in the lower house of parliament.

Abe said his friend Kotaro Kake had not asked for his help, and nor had he helped his friend in the matter of setting up the school.

"I would like to clearly state that there was no mention or consultation regarding the veterinary school from him [Kake]," Abe said.

"He fully understands that you cannot call each other friends if they use the position of their friends."

Kihei Maekawa, former vice minister of Japan's Education Ministry, who has indicated that Abe's influence was used to pass the ministry's approval to build the school, kept his stance at the session.

Scores of ministry documents showed the alleged pressure for an early approval of Kake's application came from the "top levels" of the Prime Minister's Office, Maekawa had claimed.

Abe is expected to reshuffle his cabinet soon after seeing public approval sink following various scandals and his ruling Liberal Democrats' railroading of unpopular legislation.

The party suffered a historic defeat in the Tokyo assembly election in early June amid favouritism allegations and a gaffe by a cabinet minister.