Dense fog in the downtown area forced dozens of flights to San Diego International Airport (SAN) to be delayed or diverted overnight.

About 28 flights to the airport were either delayed or diverted late Monday and early Tuesday, according to flight tracking software.

NBC 7 Meteorologist Sheena Parveen said a thick blanket of fog moved into the airport for a brief period overnight but cleared before 4 a.m.

SAN spokesperson Jonathan Heller confirmed there were some flight delays due to weather. Planes in the air were landing in reverse, from west to east, to avoid the clouds of fog while planes on the ground waited to take off until inbound planes landed, Heller said.

Some flights were left circling above the airport awaiting the go-ahead to land; others were diverted to Los Angeles International (LAX), Ontario International Airport or airports in Phoenix and Las Vegas, according to the flight tracker.

SAN said the runway was also scheduled for a planned hard closure beginning at midnight until 5:30 a.m.

Travelers took to social media to lament the delays.

"Fell asleep on my flight to San Diego... woke up landing in LA.. Wasn’t dreaming, didn’t sleep through connection... apparently it was too foggy so they turned around," Twitter user @jakebohall said.

Twitter user @meganranney said her late night flight was diverted to Ontario.

"My airplane was diverted from San Diego due to fog. Now in Ontario CA awaiting next steps." About an hour later, the user tweeted, "Ugggghhhh just landed in Los Angeles. 2 hours after I was supposed to land in San Diego."

Max Do told NBC 7 his flight from Hawaii was also delayed to LAX. Travelers on his flight were told they would need to be bussed back to San Diego.

No other information was available.

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