Investigations have been launched into Friday's power outage at London's Heathrow Airport, with both the airport's board and the United Kingdom's energy authorities examining the crisis that stranded hundreds of thousands of travelers worldwide.

Heathrow board member and former transport secretary Ruth Kelly will lead an internal review of the airport's emergency response, while Energy Secretary Ed Miliband has ordered the National Energy System Operator, or NESO, to investigate the electrical substation fire that triggered the shutdown.

In addition, London's Metropolitan Police said its counter-terrorism unit, with its rapid-response capabilities, is leading and coordinating its security-related inquiries, though it emphasized the incident is not being treated as suspicious.

The fire at a substation in west London forced Europe's busiest air hub to cancel more than 1,300 flights on Friday, affecting an estimated 300,000 passengers globally and drawing fierce criticism from industry leaders and lawmakers, news agencies reported.

While Heathrow declared itself "fully operational" by Saturday, airlines warned that disruption would continue for days as they work to reposition aircraft and crews, leaving thousands of passengers still scrambling to reach their destinations.

Miliband emphasized the government's commitment to preventing future disruptions.

"We are determined to properly understand what happened and what lessons need to be learned," Miliband said on Saturday.

"I have today commissioned the NESO to carry out an investigation into this specific incident and to understand any wider lessons to be learned on energy resilience for critical national infrastructure, both now and in the future," he added.

The Department for Energy Security and Net Zero said the NESO investigation would build a "clear picture" of the incident and UK's energy resilience to prevent it "from ever happening again". Initial findings are expected within six weeks, it said.

Labour Party politician Toby Harris, who leads the National Preparedness Commission, said: "This is a huge embarrassment for Heathrow airport. It's a huge embarrassment for the country that a fire in one electricity substation can have such a devastating effect."

The chief of logistics and supply chain company PS Forwarding, Jason Bona, told the BBC's Today radio program the incident had made Heathrow a "laughing stock" in the global freight community.

Defending the airport's response, Heathrow CEO Thomas Woldbye told the BBC he was "proud" of how staff handled the "major incident". He explained that while backup systems exist, they're "not designed to power the entire airport", which he said consumes as much energy as a city daily.