Farmer Ngo Van Hung has two hectares of lychee. He said in 30 years he had never seen such a poor crop.

"I follow the same techniques as previous years but maybe the unfavourable weather is the issue," he said.

Another farmer, Tran Van Lan, 57, has 2.50 hectares of lychee with over 1,000 trees. This year the trees have few flowers, and around a fifth of the usual amount have blossomed. He estimated that this year's output may fall to just two tonnes.

"We harvested nearly 40 tonnes of lychee last year and earned VND300 million in profit," Lan said. "With this year’s poor crop, we’ll just cover production."

Thanh Hai Agriculture Collective Director Ngo Van Lien said their 16 members work on over 50 hectares of lychee. Their trees have also produced just a handful of blossoms and some have no flowers.

"We harvested hundreds of tonnes of fruit last year but this year's output might be about 4-5 tonnes," he said. "The warm weather may be the cause."

Speaking with Tien Phong Newspaper, Deputy Head of the Bac Giang Provincial Plant Protection Department, Nguyen Anh Hoang said the province's lychee output this year is estimated to fall to 100,000 tonnes or 50 percent compared to last year's season.

"The warmer weather this year is the main cause," Hoang said. "The trees are producing more buds than flowers during warm weather."