Some of the islands' communications and power have now been restored, but the internet may be out for a while longer because of damage to an undersea cable.
After the eruption, Tonga's main island was blanketed in ash and its western coastline is said to be devastated.
"We're getting sketchy information, but it looks like the cable has been cut," the Southern Cross Cable Network's networks director Dean Veverka told the AFP news agency.
