A nationwide blackout in Sri Lanka has been blamed on a monkey that intruded into a power station south of Colombo.

Power is gradually being restored across the island nation of 22 million people, with medical facilities and water purification plants being given priority.

"A monkey has come in contact with our grid transformer, causing an imbalance in the system," Energy Minister Kumara Jayakody told reporters.

The blackout started at about 11:00 local time (05:30 GMT) Sunday, forcing many to rely on generators. Officials say it may take a few hours to get power back.

On social media, people criticised the authorities while making fun of the incident.

"A rogue monkey knocked out Sri Lanka's entire power grid after triggering a total failure at a substation in Colombo," X user Mario Nawfal wrote.

"One monkey = total chaos. Time to rethink infrastructure?" he added.

Another X user, Sreeni R, posted an illustration of Hanuman, a Hindu god with the face of a monkey.

"Sri Lanka tasted monkey business in the past," he wrote.

"Only in Sri Lanka can a group of monkeys fighting inside a power station cause an islandwide power outage," wrote Jamila Husain, editor-in-chief of local newspaper Daily Mirror.

In a report published on Monday, the newspaper said engineers have been warning consecutive governments "for years" to upgrade its power grid or face frequent blackouts.

"The national power grid is in such a weakened state that frequent island-wide power outages maybe expected if there is a disturbance even in one of our lines," it quoted an unnamed senior engineer saying. (BBC)