By Kiyoshi Takenaka and Sakura Murakami

TOKYO (Reuters) - Japan warned on Thursday that a new wave of coronavirus infections appeared to be spreading rapidly and urged people to take special care ahead of an approaching long weekend and school summer vacations.

Tokyo's 16,878 new cases on Wednesday were the highest since February, while the nationwide tally rose above 90,000, in a recent surge of COVID-19 infections to levels unseen since early this year. The Japanese capital marked 16,662 new cases on Thursday.

In his first news conference since former premier Shinzo Abe was killed and after the ruling coalition won an election on Sunday, Prime Minister Fumio Kishida said the highest level of caution was needed.

"The coronavirus is spreading throughout the nation and through all age groups," he said, urging people to make sure they got their booster shots - especially those in their 20s and 30s, whose vaccination rate is lagging.

"With summer vacations coming up, interaction between all generations will be increasing."

Additional steps included making fourth shots available to a wider range of people and establishing free testing sites at railway stations and airports, he said.

But he added that the number of people who were seriously ill and deaths still remained low, and that no restrictions on movement were needed at this time.

The capital, Tokyo, raised its alert level to the highest tier.

The BA.5 variant accounts for more than half of the new cases.

"Tomorrow, we will hold a meeting ... to decide on measures to be taken this summer," Tokyo Governor Yuriko Koike told a meeting earlier on Thursday, adding that the gathering would weigh expert opinion and the nationwide trend.

Kishida also paid tribute to Abe, slain at an election campaign rally last Friday, and said Japan would hold a state funeral for him in the autumn, a reflection of his international stature and contributions to Japan.