Vodafone will make all phone calls and text messages to the Soloman Islands free for its New Zealand-based customers from April 4 until the end of April 6.

The decision follows last week's magnitude 6.0 earthquake which occurred at the same time as a tropical storm. The disasters triggered extensive flooding. Authorities reported on Wednesday that half of the nation's capital, Hoiara, is without power. Confirmed casualties have exceeded two dozen.

Credits apply to all mobile, residential, and business calls made to landlines and mobile phones in the Solomon Islands, and will be applied to customers' accounts.

"Our thoughts are with the people of the Solomon Islands affected by this disaster," Vodafone NZ consumer director, Matt Williams, said.

"We hope that these measures will go some way to helping Kiwis keep in touch with loved ones in the Solomon Islands at this difficult time."

Kiwis looking to contribute to the relief effort are encouraged to do so via the Red Cross web site