(CNN) Japan's fertility crisis is worsening, with data from the first seven months of this year showing the sharpest drop in births in 30 years, according to preliminary government data.

Births fell 5.9% from January to July year on year, as the pool of women of childbearing age shrinks and more women delay having children or decide not to have them at all, figures from the Ministry of Health, Labor and Welfare show.

During this period, the total number of births was 518,590. For the whole of 2018, the official tally of births was 918,397, a figure which however excludes babies born to foreigners in Japan and Japanese babies born abroad.

The decline in births is "happening faster than official projections had envisioned," said Yasushi Mineshima, a spokesman for the National Institute of Population and Social Security Research.

Japan's birth rate has been falling since the late 1970s. In 2005, it reached a record low of 1.26, but then seemed to be on a path of recovery until it started to fall again in 2016, according to government figures . By 2018, it was at 1.42.