“We believe we will move past the key bottlenecks we’re experiencing in the next few months with further improvement in the second half,” Lucid Chief Executive

Peter Rawlinson

told analysts during a conference call.

The startup also said it delivered 125 cars in the fourth quarter after starting sales in late October. That was short of a

Morgan Stanley

estimate of around 200 cars.

Despite the cut in forecast output, Lucid continues to add more factory space, confirming plans Monday to build a second assembly plant in Saudi Arabia.

Lucid said it signed an agreement with the Saudi government to construct a plant that eventually will be able to produce 125,000 cars annually. The Newark, Calif.-based company is also expanding its lone factory in Arizona, saying a 2.9 million square-foot expansion is on track.

Fourth-quarter net losses widened to $1.05 billion, from $311 million a year earlier, as the company ramped up production and delivered its first vehicles. It lost $2.58 billion for the year, compared with a $720 million loss a year earlier.

Lucid shares, which rose 10% Monday, traded down about 13.5% in aftermarket trading following the release of its fourth-quarter results.

Rival electric-vehicle startup

Lordstown Motors Corp.

RIDE -19.94%

also reported heftier losses Monday and said it would need to raise more funding as it works to launch sales and production of its first electric pickup truck later this year.

The results sent the company’s stock down 20% to $2.57 on Monday.

Lucid and Ohio-based Lordstown Motors are among a handful of electric-vehicle startups whose valuations have tumbled in recent months, after going public last year amid surging investor enthusiasm for EVs.

Lucid, whose largest shareholder is the Saudi Public Investment Fund, has attracted investor attention with the rollout last fall of its first vehicle, the Lucid Air sedan.

The fully electric car, priced from $77,400 to around $170,000, delivers an industry-leading 520-mile range on a single electric charge for its top model. MotorTrend magazine awarded the Air sedan its coveted Car of the Year award for 2021, adding to the startup’s buzz.

Shares have cooled in recent months, though, along with other EV newcomers, like

Rivian

Automotive Inc. who face steep challenges in ramping up production, analysts say. Lucid shares have fallen about 24% this year.

Lucid has said it is using more than $4 billion in proceeds from a reverse merger deal last July that took it public and other investments to expand the Arizona plant’s production capacity, as well as build out its network of retail sites and service centers.

The competition race in the electric-vehicle market has continued to intensify this year with traditional car companies now producing more plug-in models and startups like Lucid and Rivian putting out their first offerings.

Unlike Lucid, Lordstown Motors hasn’t yet begun full-scale manufacturing. It has faced scrutiny in the past year over how it reported prospective orders and its ability to bring its vehicle designs into production.

The company’s chief executive and chief financial officer resigned last June as those challenges mounted for the aspiring auto manufacturer.

Lordstown, which released its results for the three months through December on Monday, reported no sales last year. Its net loss of $81.2 million in the fourth quarter, or 42 cents a share, was steeper than the company’s loss of 37 cents a share a year earlier.

Adam Kroll,

Lordstown’s chief financial officer, said that the company would have to raise more money to launch its Endurance electric pickup truck.

It still expects the truck to launch commercially in the third quarter of 2022, with as many as 500 vehicles produced this year. Up to 2,500 Endurance trucks could be sold next year, Lordstown said.

Write to Mike Colias at Mike.Colias@wsj.com and Matt Grossman at matt.grossman@wsj.com