By Liz Hampton and Erwin Seba

HOUSTON (Reuters) - A 300-ton crane at a Torrance, California, refinery that Exxon Mobil Corp plans to sell fell onto a portion of a gasoline unit at the plant, industry sources said on Monday.

Three workers escaped with minor injuries as the crane toppled over while lifting a reactor top for the 100,000 barrel per day (bpd) gasoline-producing fluidic catalytic cracking unit (FCCU) at the 149,500 bpd refinery.

The damage to piping, the crane and time needed to clear it away could delay by weeks the refinery reaching 15 straight days of normal operations as required by the sales agreement signed in September with PBF Energy, which is to pay $537.5 million for the plant.

PBF was "working with Exxon to understand the impact of today's incident on refinery operations," PBF spokesman Michael Karlovich said. "We continue assessing Torrance refinery operations and will update our prior statements on the transaction if and when appropriate."

Exxon spokesman Todd Spitler said the sale was on track.

"Change in control still remains mid-2016," Spitler said in an email.

Spitler also said operations at the refinery were normal following the crane's collapse at about 9:30 a.m. PDT (1630 GMT) on Monday.

Following the collapse, the refinery's safety flare system was tripped at 9:39 a.m., according to a notice Exxon filed with the South Coast Air Management District.

"The Torrance refinery submitted an unplanned flaring notification to the South Coast Air Quality Management District due to a breakdown in some units," Spitler said. "The unplanned flaring notification was unrelated to the crane incident. Operations are normal; no impact to production."

The flaring was the result of breakdowns in some units, Spitler said.

Energy industry intelligence service Genscape said the refinery appeared to be operating normally following the flaring.

Sources familiar with refinery operations said it was unclear when the FCCU would resume full production and continues to operate at reduced throughput.

Wholesale gasoline prices jumped 5 cents a gallon to sell at 20 cents a gallon over July NYMEX gasoline futures in the Los Angeles market, traders said on expectations gasoline production remained cut back at Torrance.

Most sale agreements like that between Exxon and PBF expire six months after the deadline, which the companies said was the second quarter of this year.

The FCCU restarted in early May after being shut for 15 months following a fire and explosion in February 2015.

(Reporting by Liz Hampton, Erwin Seba in Houston; Jessica Resnick-Ault and Jarrett Renshaw in New York; Editing by Bernard Orr and Leslie Adler)