"The UAE has entered a landmark phase today," tweeted Sheikh Mohammed bin Rashid Al-Maktoum, the Emirates' vice president and prime minister.

"The first megawatt from the first Arab nuclear plant has entered the national power grid," said Sheikh Mohammed, who is also the ruler of Dubai.

Abu Dhabi Crown Prince Sheikh Mohammed bin Zayed Al-Nahyan too lauded the "historic milestone".

"The start of commercial operations at the Barakah nuclear energy plant is a historic milestone for the UAE that significantly enhances the sustainability of our entire power sector," he tweeted.

The UAE, which is made up of seven emirates, including the capital Abu Dhabi and freewheeling Dubai, is the fourth largest oil producer in the OPEC cartel.

The country was built on oil, but is spending billions to develop enough renewable energy to cover half of its needs by 2050.

When fully operational, the four reactors of the Barakah plant will generate 5,600 megawatts, around 25 percent of the UAE's electricity needs.

The plant started up in August when authorities pushed the button on the first of four reactors.

Barakah, which means "blessing" in Arabic, is an Arab first.

Saudi Arabia, the world's top oil exporter, has said it plans to build up to 16 nuclear reactors, but the project has yet to materialise.

Barakah -- on the Gulf coast, west of Abu Dhabi -- was built by a consortium led by the Korea Electric Power Corporation at a cost of some $24.4 billion.

Across the Gulf, Iran operates a Russian-built nuclear power plant at Bushehr on its southern coast.