A US judge has blocked an order from Texas' governor cutting the number of sites voters can drop off mail-in ballots for November's presidential election, which Democrats had said amounted to voter suppression.     

The order, issued in early October by Republican Governor Greg Abbott, limited the number of drop-off centers to one per county, even as mail-in voting is expected to become much more popular due to the coronavirus pandemic.

The move would help curb "illegal voting," Abbott had said, in line with views expressed by President Donald Trump, who frequently claims without evidence that postal ballots are a source of massive vote fraud.

But in a decision published Friday following a challenge by voting rights advocates, federal judge Robert Pitman blocked the order, arguing it "restricts the rights of some voters, those who qualify to vote absentee in larger, more populous counties."

The order also added to voter confusion, Pitman's 46-page decision said, and would force voters to travel further to cast their ballot and wait in longer lines to vote, leading to greater risks of exposure to the virus. Claims that the order would reduce voter fraud had no "factual support," he added.

Texas -- a Republican stronghold, but where Democrat Joe Biden is threatening -- has some of the most populous counties in the country. More than 2.3 million voters live in Harris County, which includes Houston.

Under Abbott's order, 11 of its 12 drop-off points had been scheduled to close. The Texas Democrats tweeted that the blocking of the order was a "big win for Texas voters."

"Frankly, it ought to be a shock to all of us that such a ruling is even required," Democratic Party Chair Gilberto Hinojosa said, according to local paper the Austin American-Statesman. The state's attorney general was likely to appeal the ruling, it added.

Mail-in votes can be dropped off at dedicated ballot boxes as an alternative to using the under-pressure postal service. The practice is seen as safer for the elderly and others at higher risk from Covid-19 if they go to a polling station.

Apart from isolated incidents, no serious study has reported major fraud related to postal ballots in a US election. Voting by mail was widespread during the 2016 presidential race, where nearly a quarter of the votes (33 million) were mailed in.