The Cuban activist Oswaldo Payá, who spent decades speaking out against the communist government of Fidel and Raúl Castro, has died in a car crash. He was 60.

Payá and a Cuban man described by media as a fellow activist, Harold Cepero Escalante, died in a one-car crash in La Gavina, just outside the eastern city of Bayamo, Cuban authorities said. A Spaniard and a Swede also riding in the car were injured.

Witnesses said the driver of the rental car lost control and struck a tree, according to Cuba's International Press Centre. Police are investigating.

"This Sunday has been a day of mourning. A terrible tragedy for his family and a loss for the opposition movement," said Elizardo Sánchez, a human rights advocate and de facto spokesperson for Cuba's small opposition. "He was a prominent leader. He dedicated years of his life to fighting for democracy."

Payá's home is in Havana and it was not immediately clear why he was near Bayamo, 500 miles east of the capital.

He is the second leading Cuban dissident to die in the past year, after Laura Pollan, co-founder of the protest group Ladies in White, died of heart failure in October.

Payá, who drew strength from his Roman Catholic roots as he pressed for change in his homeland, continued to voice his opposition after Fidel resigned because of illness in early 2008. He called the passing of the presidency to younger brother Raúl a disappointment.

"The driving force of society should be the sovereignty of the people, not the Communist party," Payá wrote after the new parliament chose Raúl as head of state and government. "The people of Cuba want changes that signify liberty, open expression of their civil, political, economic and social rights."

Payá, an electrical engineer, gained international fame as the top organiser of the Varela Project, a signature-gathering drive asking authorities for a referendum on laws to guarantee civil rights such as freedom of speech and assembly.

Shortly before the former US president Jimmy Carter's visit to Cuba in May 2002, Payá delivered 11,020 signatures to the island's parliament. He later delivered a second batch of petitions containing more than 14,000 signatures to the National Assembly, Cuba's parliament, posing a renewed challenge to the island's socialist system.

The Varela Project was seen as the biggest non-violent campaign to change the system the elder Castro established after the 1959 Cuban revolution.

The government set aside the first batch of signatures and launched its own, successful petition drive to enshrine the island's socialist system as "irrevocable" in the Cuban constitution.

Payá continued his efforts, saying it was more important to mobilise Cubans to demand human rights than to win government acceptance of the project. However, his influence waned notably in his final years as younger activists and bloggers such as Yoani Sánchez gained international headlines.

Payá and other long-time opposition figures were described disparagingly in leaked, confidential US diplomatic cables as old, riven by petty rivalries and out of touch with the island's youth. "They have little contact with younger Cubans and, to the extent they have a message that is getting out, it does not appeal to that segment of society," said one cable from 2009, which was made available by WikiLeaks the following year.