NEW YORK • The toughest security presence in years will be in place to safeguard New Year's Eve festivities in New York's Times Square, where around two million people are expected to congregate, police said.

The stepped-up security follows two recent attacks, both apparently inspired by the Islamic State in Iraq and Syria (ISIS) extremist group - an aborted bombing in a subway tunnel on Dec 11, and a truck attack in TriBeCa that killed eight people on Oct 31.

New York police chief James O'Neill on Thursday said there were no direct, credible threats, but promised people would see a "stronger police presence out there than we have seen even in recent years", which he called "prudent" in the wake of recent incidents.

This year, the New York Police Department (NYPD) will issue a tactical bulletin and training video to all officers involved in the security operation.

"We owe it to the cops to give them some kind of guidelines," the NYPD's chief of counterterrorism James Waters told a news conference, two days before the annual dropping of the New Year's ball at the famed mid-Manhattan crossroads. The video and bulletin will include instructions on protecting bystanders if officers suspect someone has a bomb, and guidance on apprehending and disarming suspects with the assistance of the bomb squad, he said.

Last May, a US Navy veteran, with no apparent terror motive, rammed a car into Times Square, killing a young woman and injuring 22 other people. The authorities are also guarding against a Las Vegas-style shooting, after a sole gunman holed up in a high-rise hotel shot dead 58 people at a country music festival on Oct 1, the worst mass shooting in recent US history.

Mr O'Neill said there would be more bomb-sniffing dogs, more counter-sniper teams and more officers on the ground than last year, but declined to set a number.

Concrete, blocker vehicles and sand trucks will seal off Times Square, trucks will be restricted, and spectators will have to walk through two layers of checkpoints to access the area, subject to bag checks and screenings to ensure no weapons.

Heavy-weapons teams and dog patrols will be deployed throughout the area and uniformed police will work hand-in-hand with security at every hotel in the area.

Police have repeatedly denied any specific threats, but said they were aware of militant propaganda urging sympathisers to attack New York and holiday celebrations.

Tomorrow is expected to be the coldest New Year's Eve in the US financial capital for 55 years.

The National Weather Service has warned that temperatures could fall to minus 10 deg C at midnight on Dec 31, the coldest since 1962.

AGENCE FRANCE-PRESSE, REUTERS