Dr Bloomfield is also giving the latest update on the port worker who tested positive for Covid-19 last week.
The marine electronics engineer is the first community case in New Zealand since September 24.
Test results of close contacts of the port worker, including one workplace contact and two of four household contacts, had tested negative, Dr Bloomfield said.
Two other household contacts were still awaiting test results.
He said the most likely source of infection was a ship on which the man worked on in Auckland.
The ship travelled from Brisbane to Tauranga and then to Auckland, where eight crew joined it from the Philippines.
The man had worked on the ship while it was in Auckland. He was wearing PPE while on board.
The ship then went to Noumea and is on its way to Brisbane.
Dr Bloomfield said he was interested to see if any workers on board will test negative.
A second ship, which operated only in NZ waters and with a NZ-based crew, was also a possible source of infection.
That ship is currently anchored off Napier and all 21 workers on board are being treated as close contacts. The man had been working on equipment on the ship.
Crew members were receiving daily health checks, Dr Bloomfield said.
Genomic sequencing said the strain of Covid-19 has not been previously seen in New Zealand and was not linked to the recent August outbreak, he said.
Dr Bloomfield said there were 29 close contacts, including 21 on the ship off Napier, four household contacts, three port workers, and one workplace worker.
All would be in isolation for 14 days.
Options were being considered for testing the 21 people on the ship. A helicopter could pick them up or the ship could be sent to Auckland. Napier port did not want the ship to berth, Dr Bloomfield said.
Pop-up centres were being set up in Auckland and in Taranaki for people to be tested if they wanted. Staff in hotels where the man stayed in New Plymouth were also being tested.
The infected worker was being tested fortnightly, and Dr Bloomfield said one thing to look at was whether such workers should be tested two to three days after finishing a long shift working on a ship.
He said a shorter period of time on the ship for workers could also be looked at.
Overall there have been 1530 confirmed cases in New Zealand, with 37 currently active cases.
Yesterday there were 1373 tests conducted.
Dr Bloomfield said the current port measures were "very good" and included regular testing, including those who accessed ships.
But the entire process would be looked at to see if anything needed to be improved.
No need to change alert levels
Prime Minister Jacinda Ardern said yesterday there was no need at this point to change alert levels, and that border controls were working as they should because the port worker was being regularly tested.
Those tests had all come back negative, and he was due for his next test on Friday.
But he had become ill three days ago, on Friday, called Healthline, and was tested later the same day.
A positive result was returned on Saturday. Bloomfield informed Health Minister Chris Hipkins just after 6pm, less than an hour before voting stopped.
Bloomfield said yesterday that the man was potentially infectious on Wednesday and Thursday, when he was working in New Plymouth on a ship at the port.
He had driven by himself from Auckland to New Plymouth on Tuesday, stayed in two rooms while there which have since been deep-cleaned, and then driven back to Auckland on Wednesday evening.
"So far there is no evidence of any onward community transmission," Bloomfield said yesterday.
His four household contacts have been tested and are in isolation.
The only people he interacted with at the port were security and people on the ship, Bloomfield said, and close contacts were being sought.
Three Port Taranaki workers were isolating at home while awaiting test results. The ship remains anchored off Napier's coast. The Ken Rei logging ship was due to load logs in Napier and is carrying 21 crew.
A Napier Port spokesperson confirmed that the ship had remained offshore overnight and had not been into Napier Port.
"Our position remains that the ship should stay anchored offshore. We will await further instructions and assist public health as necessary."
A pop-up clinic was being set up at Port Taranaki today for anyone who wanted to be tested.
