Sri Lanka plunged into darkness on Sunday as a nationwide power outage caused massive losses to businesses and wiped millions from the economy.

The reason behind one of the worst power outages in the island nation’s history, authorities said, was a monkey.

The outage began at around 10.45am local time and continued for several hours before it was restored by the national electricity board, which prioritised medical facilities and water purification plants. The supply was eventually restored at around 6pm.

The Ceylon Electricity Board initially said the power cut was caused by an emergency at a substation south of the capital Colombo, without providing further details.

Later, energy minister Kumara Jayakody said a group of monkeys had jumped into the Panadura Power Station during a scuffle and one of them landed on the transmission line. “A monkey has come in contact with our grid transformer causing an imbalance in the system,” the minister was quoted as saying by AFP.

A security guard at the power station claimed that he heard a loud explosion and saw a ball of fire. He said it was unlikely a monkey could have caused such as a crisis.

“Monkeys jump into the power station very often. This does not seem to have been caused by a monkey,” the guard told the Daily Mirror paper.

The energy ministry apologised for the inconvenience caused to the South Asian nation’s 23 million people.