LISBON — A British prisoner is among five inmates who have escaped from a high-security prison in Portugal.

A search is continuing for Mark Cameron Roscaleer and four other prisoners after they broke out of the Vale de Judeus jail about 43 miles (70km) north of the capital Lisbon on Saturday.

They escaped by scaling the wall with a ladder and had "external help", the Portuguese prison service said, according to Reuters news agency.

Roscaleer is serving a nine-year prison sentence for kidnap and robbery, Portuguese media report.

Vale de Judeus is a high-security prison with a capacity of 560 inmates, according to its website.

The prison service said the escape happened on Saturday morning, at 10:00 local time (09:00 GMT).

As well as Roscaleer, the five inmates included two Portuguese men, an Argentinian and a Georgian, Portuguese media say.

The two Portuguese escapees were serving 25-year sentences for offenses including drug trafficking, criminal association, theft, robbery and kidnapping, Portugal's prison service told Reuters.

The other three had been convicted of offenses such as theft, kidnapping and robbery.

Portugal's national union for prison guards — the Sindicato Nacional do Corpo da Guarda Prisional (SNCGP) — shared mugshots of the five on social media.

Frederico Morais, the head of SNCGP, told Portugal's SIC Noticias news channel that the inmates were extremely dangerous and the public should not approach them.

Morais also said the escape happened due to a lack of prison guards, which meant the surveillance towers were not manned, the Portuguese news site Diario de Noticias reported.

The prison service said the men escaped "with external help through the launch of a ladder, which allowed the inmates to scale the wall and access the outside".

Portuguese police have reportedly asked for international cooperation to capture the five inmates.

The BBC has contacted the UK Foreign Office. — BBC