With growing concern over Hawaii’s potential vulnerability to North Korean ballistic missiles, plans are being fast-tracked for a new medium-­range radar here, while a Pentagon official confirmed that a new U.S. defensive missile being developed jointly with Japan could add a second layer of defense for the state.

A total of 36 ground-based interceptors in Alaska and California defend Hawaii — and the mainland — against North Korean missiles. However, Hawaii’s proximity to North Korea — 4,660 miles — means an enemy missile would arrive in just 20 minutes and limits what officials call a “shoot, look, shoot” second chance for success.

At a congressional hearing last week, Vice Adm. James Syring, director of the U.S. Missile Defense Agency, was asked about the defense of Hawaii and potential use of the new Raytheon Standard Missile 3 Block IIA — which comes from a line of ship-based missiles — against North Korean threats.

“We’ve done the analysis and looked at that extensively,” Syring said of the missile, which as well as a larger kinetic warhead has a wider airframe and new second- and third-stage motors that are expected to allow it to defend broader areas from ballistic missiles.

There is “inherent capability to engage longer-range threats,” and while the missile hasn’t been tested in such a capacity, “analysis indicates that that could add another layer of defense to Hawaii,” Syring said Wednesday at the hearing on missile defense.

Riki Ellison, chairman of the Missile Defense Advocacy Alliance, a Virginia nonprofit that seeks a strong missile defense, favors activating the Aegis Ashore land-based missile test facility on Kauai in times of emergency to better protect Hawaii. The Pearl Harbor destroyer USS John Paul Jones previously test-launched an SM-3 Block IIA missile off Kauai and is expected to do so again in the near future.

“That (missile) should be one of the systems that we look at to see what’s best for the defense of Hawaii,” Adm. Harry Harris, head of U.S. Pacific Command on Oahu, said during congressional testimony in April.

With the threat from North Korea escalating — and Hawaii much closer than the West Coast to the rogue nation — a new “Homeland Defense Radar — Hawaii” also is planned for the state.

Officials are hoping the new radar, which would help cue ground-based interceptors in Alaska and California, can reach initial operating capability in 2023 to augment or replace the floating Sea-Based X-Band Radar, which needs to go into dry dock for repairs in a few years and ultimately might be moved elsewhere.

Within the Missile Defense Agency’s $7.9 billion fiscal 2018 request are $130.7 million for the SBX and $21 million to conduct site selection and other preliminary work on the Hawaii radar.

“To address the continued missile test activity of North Korea, our budget request includes funds to extend (the SBX’s) at-sea time from 120 to 230 days at sea and conduct contingency operations for defense,” Syring said in written testimony.

There are “six or seven locations we’re looking at” in Hawaii for the radar, Syring said. The Pacific Missile Range Facility on Kauai is one option, he said. Ellison estimates the radar and related systems could cost $1 billion.

In the short term, Ellison advocates installing an AN/TPY-2 missile-defense radar in Hawaii that can detect, classify and track ballistic missiles, and emergency activating Aegis Ashore on Kauai with SM-3 IB and eventually IIA missiles.

An Aegis Ashore defensive site is in operation in Romania and will be in Poland in 2018, while Japan is looking at installing up to two Aegis Ashore sites.