More than 400 schools across England have received hoax bomb threats believed to be coming from the US.

Humberside police said that schools and colleges across the country, including 19 in its region, had received emails “claiming a device has been planted and demanding cash”.

Det Supt Tony Cockerill, of Humberside police, said: “We have been liaising with our counter-terrorism colleagues across the country and it is not believed that the threats are credible.

“We have spoken to all schools who have contacted us, reassured them that there is no need to evacuate and offered them security advice.”

Northumbria police said more than 35 schools in its region had received emails threatening to detonate a bomb unless money was handed over.

A police spokeswoman said detectives had assessed there was “no viable threat” and that no schools in the area had been evacuated.

The force said in a statement: “We have received reports from a large number of schools in our region that they have received threatening emails.

“The emails inform the school that a bomb has been placed on the grounds and will be detonated if they don’t hand over cash.

“Detectives have looked into the emails – which appear to originate from the US – and can confirm that there is no visible threat.”

Police officers visited the schools to reassure pupils and staff. “We take all incidents of this nature extremely seriously and an investigation into the emails in question is under way,” the spokeswoman said.

In London, some schools were evacuated after receiving what the Metropolitan police described as “malicious communications”.

Kantor King Solomon school in Barkingside, east London, said it briefly evacuated pupils but later established there was “no further threat”.

There was a national threat made to lots of schools this morning and KKS went into invacutation to ensure the safety of our site.This was in conjunction with CST and the Metropolitan Police. We have established that there is no further threat and School is now running as normal. — Kantor King Solomon (@kingsolomonhigh) March 19, 2018

A Met spokeswoman said the force was looking into the threats.

She added: “Police are investigating reports of communications made to a number of schools across London today, Monday, 19 March. There have been no arrests. Inquiries are ongoing.”