Apple and Facebook are reportedly offering to pay up to $20,000 for female employees to freeze their reproductive eggs, in a bid to hold on to their best workers.

The companies are covering up to $20,000 for the procedure and annual storage costs, NBC said, citing sources at the Silicon Valley firms.

"We continue to expand our benefits for women, with a new extended maternity leave policy, along with cryopreservation and egg storage as part of our extensive support for infertility treatments," Apple said in a statement.

Apple recently introduced new benefits including extended parental leave, while Facebook said it offers four months of paid leave for both new mothers and fathers.

"We want to empower women at Apple to do the best work of their lives as they care for loved ones and raise their families," the tech giant said.

Queried about the reports by AFP, Facebook and Apple declined to comment.

Egg freezing is an increasingly popular way to delay child bearing. It costs about $US10,000 initially and then $500 each month after that.

In the raging war for talent, Silicon Valley companies are offering an array of new family-planning perks.

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Apple said it also reimburses eligible expenses associated with the legal adoption of a child.

"Egg freezing gives women more control," said Jennifer Tye, marketing lead for Glow, a mobile application aimed at helping women avoid pregnancy or conceive.

"When I turned 30, I had this notion that my biological clock was ticking, but I didn't know what my options were.

"These employers should be commended."

Renewed pressure over diversity

According to US government data, 20 per cent of women in the country wait until age 35 to have their first child.

Around one third of women aged 35-39 have fertility problems and the proportion increases to 64 per cent when women are between 40 and 44 years old.

The moves come with tech firms facing renewed pressure over diversity in a male-dominated sector.

In recent weeks, major tech firms have been looking at the issue with "diversity reports" that examine the composition of the workforce.

Microsoft reported earlier this month that its staff was 29 per cent women. At Google, the figure was 30 per cent.

For Facebook, the percentage of women was 31 per cent, but just 15 per cent in technical jobs.

The new benefits are expected to help companies like Facebook and Apple attract more women.

At the same time, experts point out that freezing is a relatively new procedure that does not guarantee a successful pregnancy.

AFP/Reuters