A Sussex castle has been forced to suspend its operations due to structural issues.

Hertsmonceux Castle, one of the oldest significant brick buildings in England, said a number of repairs require “immediate attention”, including to the south wall of the building.

A structural engineer who visited the castle earlier this month warned that the situation was “more serious than previously understood”, with portions of the castle closed over safety fears.

Repairs are expected to take at least 12 to 18 months, with a complete survey of other areas of the castle taking place in the new year.

Due to safety concerns, the Canadian Queen’s University, which operates Bader College at the castle, has moved classes online until the end of term, with the college’s roughly 150 students returning to the university’s Ontario campus in January.

A spokesman for the university said: “Queen’s University is continuing to assess the situation and full extent of the work needed but it is clear as of now that there is at least one year to 18 months of structural repairs to undertake.

“In addition, the structural engineer has recommended a complete survey of other areas of the castle, which will be undertaken in late January or early February.

“We want to reassure our community that students are receiving close support at this time to help with their transition to the university’s Canadian campus.”

Hertsmonceux Castle said the decision was taken “out of an abundance of caution… to ensure the health and safety of students, staff and faculty.”

A spokesman for the castle said: “We realise this may be distressing news for many within the local community and those with close ties to Bader College and the castle.”

The castle, which also hosts weddings and corporate events, was built in 1441 using bricks taken from local clay by builders from Flanders.