Facebook and Apple are covering the costs for female employees to freeze their eggs to delay childbearing which could hamper their careers, NBC News reported Tuesday.

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

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

According to the online forum eggsurance.com. the procedure is gaining popularity as more women delay plans to start a family.

"Women today are at a cultural and generational crossroads. We have the same career expectations and demands as men," says a post on the eggsurance.com website.

"As our biological clocks tick away, we must establish ourselves in the workplace, find the right mate and become financially secure enough to establish a family."

According to the website, citing US government data, 20 percent of women 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 percent when women are 40-44 years old.

According to NBC, Facebook recently began covering the costs of egg freezing, and Apple will begin in January.

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 only 29 percent women. At Google, the figure was 30 percent. For Facebook, the percentage of women was 31 percent, but just 15 percent 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.