A double fuel tanker truck on Thursday swerved to avoid an oncoming truck and rolled over into a ditch off Highway 29 near Calistoga, closing a stretch of the road and snarling traffic in both directions between Napa and Lake counties.

Officials worked for hours to unload the fuel from the truck, but they didn’t know late in the evening when the roadway would reopen to traffic.

The closure started about 10:40 a.m., after CHP responded to an overturned truck near Old Lawley Toll Road. Officials shut the crucial two-lane highway that goes through downtown Calistoga and connects Lake and Napa counties. Drivers were being directed to use rural Butts Canyon Road in Pope Valley or Highway 128 through Calistoga.

The driver of the tanker truck, Paramjit Singh Kullar of Pittsburg, told authorities his rear tank slid off the roadway when he swerved to avoid a truck going the opposite direction that had crossed over the double yellow lines, said Napa-area CHP Officer Marc Renspurger. Kullar was driving north and hauling diesel and gas tankers.

“Once (the tank) started going down the hill, it pulled the first tank down with it,” Renspurger said. “The driver was wearing his seatbelt and from what I understand some passersby stopped to help him get out of the truck.”

Kullar, 71, was uninjured.

The other vehicle, a Volvo semi-truck driven by 58-year-old Kevin de Angelo of Los Angeles, was heading south and while attempting to turn left on Highway 29 veered across the yellow dividing lines into oncoming traffic. This forced Kullar to swerve right with his tanker truck to avoid a collision, officials said.

About 5 gallons of fuel leaked from the tanker truck’s gas line onto the hillside, after it toppled into the ditch. Neither of the fuel tankers leaked, however, Renspurger said.

De Angelo continued driving south and was unaware of the tanker rollover. He was stopped on Highway 128 by Sonoma County Sheriff’s deputies. No arrest was made.

The northbound lane of Highway 29 was blocked from Tubbs Lane, located about three miles northwest of downtown Calistoga, to Bradford Road, Cal Fire spokesman Will Powers said. Traffic headed south on the roadway was stopped from Bradford Road in Lake County to Tubbs Lane, he said.

“We are hoping to get this cleaned up before dark, but that is only a hope,” Renspurger said. “We have to haul out the fuel and then tow the truck up the hill.”

If crews have to work through the night, it would slow their efforts to unload the fuel from the tankers, he said.

“Two heavy-duty tow trucks are waiting nearby the scene for when the tankers are empty so that roads can reopen as soon as possible,” Renspurger said.

CHP and Cal Fire responded to the incident, along with Caltrans and California Department of Fish and Wildlife crews.

You can reach Staff Writers Alexandria Bordas at 707-521-5337 or alexandria.bordas@pressdemocrat.com. And Nashelly Chavez at 707-521-5203 or nashelly.chavez@pressdemocrat.com.