London Fire Brigade later stated that "high levels of natural gas" had been detected because of a ruptured gas main in Craven Street.
Fire crews using detection equipment have identified high levels of natural gas in the atmosphere, it said.
Witnesses said there was "chaos" as doormen at the Heaven nightclub ordered guests to leave in the early hours.
Intercontinental Hotel in Kabul under attack, Afghan official says
The hotel has not been affiliated with the InterContinental Hotels Group for decades but continues to use a variation of the name. US State Department spokeswoman Heather Nauert said it was not known if any American citizens had been caught up in the attack.
As of 8.30am, the Strand and some surrounding streets are still closed to cars, although limited pedestrian access is being permitted.
They said: "Due to a gas leak in the Strand, WC2 businesses and hotels are being evacuated as a precaution".
"We're doing everything possible to work around this and keep people moving, and will be running trains into other London stations, however there will be some unavoidable delays and cancellations this morning", a spokesperson from the Southeast assured.
"They have been found alternate accommodation", a senior official from the Indian High Commission in London said.
What Happens During a Government Shutdown?
It's not a good weekend to plan that road trip for a wintertime twirl on the ice under Half Dome in Yosemite National Park . Homestead National Monument Superintendent Mark Engler said the National Parks Service is not expecting a shutdown.
One clubber tweeted: "Evacuated from heaven because of a gas leak wow". Literally chaos. Crush on the stairs.
A rest centre has been set up for affected residents at the Queen Mother's Sport Centre in Vauxhall Bridge Road, Westminster Council said.
"Yes we were evacuated just after 3am, but there was no panic, no "security being knocked aside". I thought Work would let us work from home but nah nah". He told the BBC he was in the building when he was alerted to a smell. "The whole area smelt of gas, and we called the site engineers who came to investigate".
Apple executives offers choice to save battery life, doesn't recommend it
At the end of 2017, Apple admitted to iPhone performance to prevent shut-downs related to the device's deteriorating battery health.