By Jonathan D. Rockoff and Jared S. Hopkins

Novavax Inc. and Johnson & Johnson said Friday they have agreed to provide tens of millions of doses of their experimental coronavirus vaccines to the U.K. for undisclosed sums, as countries move to secure supplies of the shots.

Under the terms, the U.K. will fund a late-stage trial of Novavax's vaccine candidate starting this quarter evaluating the shot in the country's residents, and a contract manufacturer will make a key part of the vaccine at a plant in Stockton-on-Tees in northeast England, the company said Friday.

The contract manufacturer, a partnership between Fujifilm Corp. and Mitsubishi Corp., named Fujifilm Diosynth Biotechnologies, will also make extra supplies that Novavax could provide in other markets, the vaccine maker said.

"It is encouraging that Novavax's recent clinical data shows their vaccine triggers an immune response greater than that in patients who have recovered from the disease," said Kate Bingham, chair of the U.K. government's vaccines task force.

In a small number of healthy volunteers in early-stage testing, the Novavax vaccine generated promising immune responses and was generally well-tolerated.

Meanwhile, Johnson & Johnson said that the company agreed in principle to provide 30 million doses, with the option for an additional purchase of up to 22 million doses. The U.K. government also agreed to work with the company on a late-stage study testing its vaccine as a two-dose regimen, according to J&J.

"Ending the current COVID-19 pandemic will take a global effort, and this agreement is an important example of how we can begin to address this significant challenge through collaborative research," J&J Chief Scientific Officer Paul Stoffels said.

J&J began testing its vaccine in a small number of healthy volunteers last month, and a late-stage trial of the vaccine as a single shot could begin this fall.

The vaccines are among the most advanced in development, though not as far along as shots under development by companies including AstraZeneca PLC, Moderna Inc. and a partnership between Pfizer Inc. and BioNTech SE.

This week, Russia said it was clearing a homegrown vaccine for use by its general public, though researchers expressed concerns about the adequacy of evidence supporting the shot's safety and effectiveness.

The U.K., the U.S. and other countries have been reaching deals worth billions of dollars with companies developing the vaccines to lock in doses should the shots prove to work safely.

The U.K. last month struck a deal with Pfizer and BioNTech for 30 million doses, after agreeing to pay AstraZeneca for 100 million doses of a vaccine the company developed with the University of Oxford.

The U.K. government is also set to receive 60 million doses of an experimental vaccine under development by Valneva SE of France.

Novavax, of Gaithersburg, Md., was founded in 1987 but doesn't have any products on the market. Its coronavirus vaccine is expected to require two shots. It is scheduled to begin mid-stage, or Phase 2, testing this month.

The company has now struck several deals with governments, companies and foundations that would see its vaccine distributed in South Korea, Japan and India, among other places.

The U.S. agreed to pay up to $1.6 billion to Novavax to fund the final stage, or Phase 3, of testing of the company's vaccine and obtain 100 million doses.

As part of the U.K. deal, Novavax said it would study the vaccine in about 9,000 adults ages 18 years to 85 years in the country, and if successful, the company would begin supplying doses as early as the first quarter of next year.

"We are honored to partner with the U.K. government to deliver a vaccine that could provide vital protection in the fight against the global health crisis," said Novavax Chief Executive Stanley Erck.

Fujifilm's plant in Billingham, Stockton-on-Tees, will make the part of Novavax's vaccine, known as an antigen, that generates an immune response. The plant will eventually produce about 180 million doses of the antigen a year, Novavax said.

Write to Jonathan D. Rockoff at Jonathan.Rockoff@wsj.com and Jared S. Hopkins at jared.hopkins@wsj.com