It was said unexpectedly by the Prime Minister that schools will close in 3 days time.
3日後 in three days time/three days from now
から from
学校 schools
閉めます will close
と突然 unexpectedly/suddenly
総理 Prime Minister
に言われました it was said by
「総理がTVでいきなり言ったとき」というのは when it was said suddenly on tv by the Prime Minister で表現することができます。
例文 It was announced on tv that you should stay at home.
「テレビで家を出ないほうがいいというのは発表された。」
参考になれば幸いです。