Telecommunications giant Telstra on Tuesday offered free telephone calls and text messages for customers wishing to check on family and friends affected by the recent earthquake and tsunami in Japan.

Telstra customers calling Japan from their fixed-line telephone or Telstra mobile phone, or sending text messages from their Telstra mobile phone, will do so free of charge between 6:00am Friday 11 March and 6:00am on Friday 25 March.

Tarek Robbiati, Group Managing Director, Telstra International Group, said Telstra was pleased to offer support to its customers during this difficult time.

"We want to help our customers who are concerned about their friends and relatives in Japan affected by the devastating earthquake and tsunami to check on loved ones," he said. "Calls and text messages to Japan will not be billed during this time."

Mr Robbiati warned that while some communication lines remained open in affected areas, customers were likely to encounter network congestion.

"We encourage customers to remain patient as difficulties and delays may be experienced when trying to connect," he said. "Sendai and surrounding areas are especially hard to reach at this time."

Mr Robbiati said in addition to providing assistance to its Australian customers, Telstra would make a $100,000 contribution to the Japanese Red Cross Society through Telstra International Group.

"At such a challenging time, it is important for businesses like Telstra to support the communities in which we operate," he said.

"Telstra has strong ties to Japan, with a number of employees based in Tokyo servicing our local customers and many employees in Australia with family and friends affected by the disaster.

"Telstra is committed to supporting its customers and the Japanese community through this emergency," Mr Robbiati said.