NASA scientists have broadcast pictures of the transit of Venus from Alice Springs to the world after cloudy skies and a mystery computer connection problem delayed the transmission.

The planned live broadcast of the rare astronomical event from an Alice Springs high school was delayed by an hour by what was later identified as an "IT problem".

Earlier, the ABC had been told that the problem was caused when a backhoe being used by a roadwork crew cut a fibre-optic cable, knocking out many internet connections in parts of the Northern Territory.

A school spokesperson says NASA computers have been connected to the school's internet system to allow the transmission to go ahead.

The transit can be seen from the NASA website and will be broadcast from Alice Springs until mid-afternoon.

Scientist Michael Johnson says Alice Springs has quickly become the main live streaming site worldwide for the transit.

"We are now getting beautiful images," he said.

He says the Alice Springs coverage was vital because another NASA site in Mongolia had clouded over and the sun had set in the United States.

"Right now, we are the main feed, coming out of Australia to NASA, so they are enjoying our images around the world," he said.

Clear skies and dry weather have made for near perfect viewing conditions in Darwin.

Hundreds of people have been watching the event through free telescopes on the city's Esplanade.

The next time Venus will be visible passing between Earth and the sun will be in 2117.

Alice Springs was one of only two locations outside the United States that was to have contributed to a live NASA broadcast of the transit of Venus across the sun.

American scientist Michael Johnson says Alice Springs was chosen because the whole six-hour event would be visible from the central Australian town.

He says NASA was intending to collate the data and compare it to previous transits.

"What makes it so special is that it is an extremely rare event," he said.

"This tiny dot that goes across the sun only happens every 105 years."

Internet and mobile services, including ATMs, across parts of the Northern Territory have been affected by the cutting of the fibre-optic cable.

Telstra says the cable was damaged late yesterday, about 17 kilometres south of Mataranka.

Spokeswoman Jane Singleton says technicians have been working to restore services.

"What has happened is roadworks ... out of Mataranka have disrupted and, in fact, severed and damaged the fibre (optic cable)," she said.

The cable has been repaired and services are being restored